Paper  Quantitative studies of the testicle 2
Embryology  27 Feb 2024 Expand to Translate 

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Bascom KF. and Osterud HL. Quantitative studies of the testicle II. Pattern and total tubule length in the testicles of certain common mammals. (1925) Anat. Rec. 159169.
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This historic 1925 paper by Bascom and Osterud compared the length of the male testis seminiferous tubule length in different species.

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Quantitative Studies Of The Testicle II. Pattern And Total Tubule Length In The Testicles Of Certain Common Mammals
K. F. Bascom And H. L. Osterud
Medical College of Virginia
Introduction
Studies of the morphology of the testicle have been largely qualitative in character. Quantitative data, however, exist with reference to gross Weight, tubule diameter, tubule length, and cell counts. As examples may be mentioned the Work of Bouin and Ancel, Hatai, Jackson, Massaglia, Latimer, and Bessesen and Carlson, who have recorded gross Weights of the testicles of various animals. Siperstein, in addition to gross weights, also gives the diameter of the seminiferous tubules and diameter of nuclei of interstitial cells. Moore, iii a later paper on experimental cryptorchidism, gives gross weights a11d tubule diameters. VVatson records seasonal changes in testicular diameter in the green ﬁnch. Riddle offers data on size and length relations in the right and left testes of the pigeon. Rasmussen, in his study of the seasonal changes in the marmot, employed cell counts of interstitial cells and records piercentage weights of the testicles. Lengths of individual tubules were determined in the mouse, rabbit, and dog by Curtis. Huber and Curtis, writing on the seminiferous tubules in mammals, mention in an incidental Way some quantitative data as to tubule length. Cunningham’s Manual of Practical Anatomy, without citing the source of information, makes the statement that the human testicle “consists of four to six hundred ﬁne hairlike tubes. . . ., each of which is about 60 cm. (two feet) long.”
To our knowledge, no quantitative method has been applied to the measurement and comparison of total tubule length of the seminiferous tubules in a series of laboratory and domestic animals. In this paper such a method and the results of its application are set forth.
Materials and Methods
Total tubule lengths of single normal testicles were computed for the following species: albino mouse, albino rat, guinea pig, cat, Belgian hare (rabbit, dog, man, pig, sheep, and bull (cow). The testicles were separated from the epididymis and other extraneous tissue and were weighed in the fresh condition before ﬁxation. In the case of certain representative testicles of the bull and pig, the tunica albuginea was stripped off and the mediastinum dissected out in the fresh condition and weighed separately from the rest of the testicle.
Bouin’s fluid was used in general as the ﬁxative, Zenker’s ﬂuid and 10 per cent formalin in a few cases. The testicles of the mouse, rat, Guinea pig, cat, hare, and dog were ﬁxed for a brief interval entire and then sliced with a razor for further fixation. From the larger testicles blocks of tissue were removed with a razor and ﬁxed. Both celloidin and parafﬁn were used for embedding, the former, to the greater extent, proving also the more satisfactory. The combination of stains most frequently used was hematoxylineosin.
The quantitative technique employed for determining total tubule length may best be presented by following successive steps in two typical examples.
Example 1. Bull testicle X3. Fresh weight, 274 grams
By the steps previously outlined it was determined that the tunica albuginea and mediastinum weighed 15.5 grams (5.6 per cent of the total weight of this testicle). Hence tubules and interstitial tissue weighed 258.5 grams.
Several representative ﬁelds in sections of this testicle were projected with an Edinger drawing apparatus and the tubules drawn in outline. Then the relative amounts of tubules and interstitial tissue present in these drawings were measured in two ways: by use of a polar planimeter and by the paper method already employed by Bascom in estimating the amounts of interstitial tissue in testicles of swine. In testicle X 3 the relative percentages of tubules and interstitial tissue were, respectively, 83.9 per cent and 16.1 per cent. Since, as already stated, tubules and interstitial tissue together weighed 258.5 grams, according to the above percentages the testicle was calculated to contain 216.88 grams of tubules. For all practical purposes the speciﬁc gravity of fresh tissue may be taken as 1.0, hence the 216.88 grams of tubules are assumed to be very nearly equivalent to a volume of 216.88 cc. or 216,880 cu. mm.
By means of a microscope with eyepiece micrometer, the average diameter of ﬁfty seminiferous tubules was found to be 0.238 mm. Using the formula 1r’l‘3, the average crosssectional area of the seminiferous tubules was calculated to be 0.0446 sq.mm. Dividing total tubule volume in cubic millimeters (216,880) by crosssectional area in square millimeters (0.0446) gives the total tubule length of this testicle in millimeters (4,862,000). This sum is more compactly expressed as 4862 meters or as 4.862 kilometers.
Example 2. Guineapig testicle. X 1.2 A. Fresh weight, 1.2423 grams
In this case the tunica albuginea and mediastinum could not conveniently be dissected away in the fresh condition. Representative transverse sections from diﬁerent parts of the testicle were prepared. By means of the Edinger apparatus, a drawing was made from "one of these sections and, with the aid of the planimeter, the percentage of mediastinum present was calculated (8.89 per cent). This was assumed to be the percentage of mediastinum in this testicle.
The volume of tunica albuginea was determined in a diiferent way.
Its thickness was measured with a11 eyepiece micrometer and found to average 0.031 mm. The Guineapig testicle approaches the spherical form rather closely. Accordingly, testicle X 12 A was assumed to be a sphere having a volume of 1.2423 cc., or 1242.3 cu.mm., the volume assumed to be equivalent to the weight of this testicle. The volume of a sphere equals 7r?°3, hence a sphere of the above volume has a radius of 6.668 mm. The thickness of the tunica albuginea (0.031 mm.) subtracted from this radius gives 6.637 mm. as the radius of the smaller sphere, with a volume of 1223.6 cu.mm., representing tubules and interstitial tissue and mediastinum.
The percentage of mediastinum in this testicle, calculated as shown above, was 8.89 per cent, equivalent to 110.4 cu.mm. Hence the net volume of tubules and interstitial tissue becomes 1223.6 minus 110.4, or 1113.2 cu.mm. Of this volume 91.83 per cent, or 1022.25 cu.mm., was seminiferous tubules, determined as in example 1. Average tubule diameter was determined by micrometer measurement to be 0.244 mm. Employing the formula 1r)‘2, the average cross—sectional area is 0.0467 sq.mm. Dividing volume of tubules (1022.25) by crosssectional area (0.0467) therefore gives 21,889 mm., or 21.889 .‘I“.l“l.(§i(3I"S as the total tubule length in this testicle.
We believe these two examples sufﬁeiently illustrate the methods by which the results to be set forth in this paper were obtained. Corrections have not been. made and could not easily be made for certain minor errors, such as assuming the guinea~pig testicle to be perfectly spherical, assuming the speciﬁc gravity of the testicle to be 1.0, or assuming that all elements of the testicle shrink equally under such technical treatment as we have employed, but we do not believe that they substantially aﬁeet our result.
Thanks are due Mr. Herman Melton for technical assistance.
Results
The numerical data obtained by the above methods are summarized in table 1.
Discussion
In table 1 the column of gross weights of testicles shows great variation in Weight in the differeiit species~——from 0.0556 gram in the mouse to 367 grams iii a bear. In View of this great; disparity in testicular weights, it is interesting to ﬁnd that the diameters of the tubules in the abovementioned testieles are, respectively, 0.191 mm. and 0.223 mm.—a (:liﬁt'e1' ‘All calculations as to percentage composition are leased on the planimeter met.hod for the sake of uniformity and because we believe it to be more accurate than the paper method. We have also found it to be more rapid and less tedious. Results obtained by applying both methods to each of twentysix testicles of animals of ten diﬁerent species show an average discrepancy between the two sets of results of 2.48 per cent, ﬁgures obtained with the planimeter method being on the average slightly higher tlian those worked out by the paper method.
In the first paper of this series (Baseom, ’:'35) no allowance was made for tunica. albuginea and mediastinum in calculating the amounts of tubules and interstitial tissue in pig testicles. relative percentages of tubules and interstitial tissue are not affected by this error, but absolute weights of these elements as given in that paper are about 8 per cent too large.
Table 1
Species and Collection Number  Gross Weight of Testis (grams)  Weight of Tubules (grams)  Diameter of Tubules (mm)  CrossSect. Area of Tubules (sq. mm.)  Total Tubule Length (meters) 

Albino Mouse  
Albino Rat  
Guinea pig  
Cat  
Belgian hare  
Dog  
Man X 10  12.21  6.577  0.1834  0.0263  249.7 
Pig  
Sheep 
ence of only 14.3 per cent. Rat testicle R 11 had a greater tubule diameter (().2654 mm.) than was found in any other testicle studied, not excepting‘ even those of the boar, bull, or ram. The smallest average tubule diameter iii the adult was found iii the human testicle X 10 (0.1834 mm.). The maxi mum va.riatie11 in tubule diameter in this series of testicles then, in round numbers, 30 per cent. There is no direct relationship betweeii tubule diameter and the size of the adult animal far as our evidence goes.
Table 2
Species  I. Meters of Tubules per gram or cubic cm of Tubules  II. Meters of Tubules per gram of Total Testicular Weight 

Mouse  31.5—35.0  27.2  30.3 
Rat (adult)  18.421.8  15.8 18.2 
Rat (immature)  46.9  30.8 
Guinea pig  21.4—24.8  17.6 21.9 
Rat (not full grown)  39.0—39.9  27.428.5 
Hare (adult)  37.8  30.4 
Hare (immature)  267.0  163.0 
Dog  27.5  29.8  22.9  25.8 
Man  37.9  20.4 
Pig  25.2 25.6  14.5 17.2 
Sheep (M 170, adult)  28.9  22.6 
Sheep (M 137, 6 mos.)  58.4  46.2 
Sheep (M 299, 3 mos.)  103.0  70.0 
Bull  22.4 ~ 32.6  16.1  23.7 
The average crosssectional area of the tubule in the rat testicle R 11 is ().0553 sq.mm.. and in the human testicle X 10 is (,).()12i(f33—ii.11 round numbers, a difference of 50 per cent.
The signiﬁcance of tubule size may perhaps be more easily grasped when expressed as in table 2, column 1, in terms of the number of meters of tubules equivalent to 1 grani in Weight or 1. cc. in volume.
Even, after allowance is made for tunica albuginea and mediast.inum, normal adult testicles Vary in relative percents ages of tubules and interstitial tissue. These variations in the species studied are summarized i11 table In each case the percentage of interstitial tissue is therefore equal to 100 minus the percentage of tubules given in the table.
Table 3 consequently indicates numerically the differences in pattern found in this series of normal adult testicles due to Varying amounts of interstitial tissue.
Table 3
Species  Percentage Of Tubules Intestis (excluding tunica albuginea and mediastinum) 

Guinea pig  89.8  97.0 
Dog  92.2  94.2 
Mouse  88.9  90.3 
Hare  89.0 
Rat  88.5  89.6 
Cat  84.5  86.9 
Sheep  84.6 
Bull  76.4  83.9 
Man  72.8 
Plg  62.2  72. 6 
Total tubule lengths for the adult animals studied are summarized in round numbers in table 4.
Incidental data exist from which total tubule length in the testicle of man and of the mouse may be calculated. Cunningham gives ﬁgures indicating a total tubule length in the human testicle of 800 to 1200 feet. Our calculation, involving a different method, gives 249.7 meters, or 819 feet.
Table 4
Species  Total Tubule Length in Meters 

Mouse  2 
Rat  20 
Guinea pig  40 
Cat (not full grown)  25 
Belgian hare  70 
Dog  150 
Man  250 
Pig  30006000 
Sheep  4000 
Bull  5000 
Huber and Curtis state that the mouse testicle contains sixteen tubules. One tubule was found to be 13 cm. in length. These ﬁgures imply a total tubule length for the mouse testicle of about 2 meters. Our ﬁgure, independently calculated, is also about 2 meters. To this extent previous data secured by methods entirely different from ours conﬁrm our computations.
At first glance the disparity in total tubule length between the larger and smaller mammals seems fairly incredible, but a little arithmetic will reveal that actually the smaller animals have a greater length of tubules per unit of body weight than do the larger ones. For example, in round numbers, a mouse would have about 1 meter of tubules per 10 grams of body weight, while a bull would have approximately 1 meter of tubules per 100 grams of body weight. If the testicle made up the same percentage of body Weight in the bull as it does in the mouse, the bull testicle would have, instead of 5000 meters of tubules, upwards of 300,000 meters. In this connection it is interesting to refer once more to table 1 and note that the mouse ha.s a tubule diameter of almost 0.2 mm., while the bull. has an average tubule diameter only 16 per cent greater (0.24 mm.). In other words, increased volume of germinal epithelium in larger testicles comes largely or wholly from increase in tubule length, not from increase in tubule diameter.
Certain immature animals are marked in table 1 with asterisks. Rat was thirty—nine days old and weighed 59.5 gmms. His testicle weight. was approximately 25 per cent that of a normal adult, but the total tubule length of his testicle was about 50 per cent that of the adult.
Rat.. R2 was siixtyvsix. days old and Weiglied 150 grams. His testicular weight. and tzubule length were almost those of the adult, although only in the earliest stages of sexual mal'l11"ll'}’.
Rat R 1 was 190 (lays old and weighed 304 grams, yet his testicular weight. and total tubule lengtxli only Sli.g’l'1tl_\' ex(e(_~e<fle(‘l those of R 2, who was onethird his age and onehalf his body weight.
iBel.gian hare 19 was less than a third grown. His testicular weight was about oneeleventh and his tubule length twoﬁ:l't.l1s that of X 18, an adult of the same species.
\I 299 was a lamb, perl1a.ps three months old. Its testicular weiglit was about. oneele\—’e11tl1 that of the adult, but its l"l'll.")'I1l(..‘. lengtll more tllau one—fo'u1‘th that of the adu'.l.t.
$10.13? was a lamb about six months old. lts t1.est.i(ular weiglit was about half that. of the adult, but its tubule length at least equal. to that of adult bill 170. QUANTITATIVE srunrus on THE TESTICLE 167
These comparisons of immature with mature testicles lead to the conclusion that total tubule length is greater in proportion to testicular Weight in the young than in the adult testicle and that adult tubule length is probably attained in the growing animal a considerable time before adult testicular Weight and adult tubule diameter have been reached.
The factors which determine testicular pattern are tubule diameter, relative amount of interstitial tissue, and amount of tunica albuginea and mediastinum. These factors are individually variable. The combined effect of their variability upon testicular pattern may be expressed numerically as in table 2, column II, in terms of the number of meters of tubules per gram of testicular weight. These data are obviously secured by dividing the total tubule length of given testicles in meters by their respective Weights in grams. This column illustrates the following points: similarity in pattern in the adult testicles of certain species, differences in pattern in the adult testicles of other species, and changes in pattern during growth in a given species. a
Summary and Conclusions
 A quantitative method is described for determining the amounts of interstitial tissue and seminiferous tubules as Well as the total length of these tubules. Testicles from animals of the following species were studied: albino mouse, albino rat, Guinea pig, cat, Belgian hare, dog, man, pig, sheep, and bull.
 The gross Weights of these testicles ranged from 0.0556 gram (albino mouse) to 367 grams (boar).
 Adult tubule diameter had a maximum variation of only 0.1834 mm. (man) to 0.2654 mm. (albino rat).
 Total tubule length in the adult varied from 1.67 meters (albino mouse) to 6312 meters (bear).
 The small variation in tubule diameter in conjunction with the tremendous differences in total tubule length indicate that space for increased volume of germinal epithelium in the larger testicles is afforded largely and sometimes wholly by increase in total tubule length, not by increase in tubule diameter.
 In spite of the great total tubule length encountered in the larger species, the smaller animals, such as the mouse and rat, actually have a greater length of seminiferous tubules per 11nit of body Weight.
 The pattern of a given testicle depends upon the relative amounts of tunica albuginea, mediastinum, interstitial tissue, and tubules, and upon tubule diameter. The combination of these factors as they occur in a given testicle may be numerically expressed in terms of number of meters of tubules per gram. of total testicular weight. This sum varies with the species studied as well as with the state of development of the individual (table 2, column II).
 Total tubule length is greater in proportion to total testicular Weight in the young than in the adult.
 Adult tubule length probably is attained in the growing animal a considerable time before adult testicular weight and adult tubule diameter have been reached.
Bibliography
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