Book - Vertebrate Embryology (1913) 2
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Jenkinson JW. Vertebrate Embryology. (1913) Oxford University Press, London.
- Vertebrate Embryology 1913: 1 Introduction | 2 Growth | 3 The Germ-Cells, their Origin and Structure | 4 The Germ- Cells, their Maturation and Fertilization | 5 Segmentation | 6 The Germinal Layers | 7 The Early Stages in the Development of the Embryo | 8 The Foetal Membranes of the Mammalia | 9 The Placenta | Figures
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Chapter II Growth
Growth may be defined as increase in size or volume. Since then growth is increase in all three dimensions of space, it is most accurately measured not by increase in some one dimension - such as stature - but by increase of mass or weight.
Growth depends upon the intake of food and the absorption of water, and exhibits itself in the form of increase of living matter or 'of secretions of watery or other substances, organic or inorganic, intra-cellular or extra-cellular, such as chondrin, fat, mucin, calcium phosphate, and the like.
That growth depends - in later stages at least - upon the intake of food is obvious. That it is due to the absorption of water has been demonstrated effectively for the tadpoles of Amphibia {Amblystoma, Rana, Bufo). The method employed was to weigh known numbers of the tadpoles at different ages, desiccate and weigh agam. The results of the investigation are shown in the accompanying figure (Fig. 1), from which it will be seen that the percentage of water rises with remarkable rapidity - from 56% to 96%- during the first fortnight after hatching. After that point the amount of water present slightly but steadily decUnes.
In later development the proportion of water slowly falls, as may be seen more fully from the tables following, for the chick and for the human embryo.
Showing the percentage of water in chick embryos at various stages up to hatching. (From Davenport, after Potts.) The table also shows the hourly percentage increments of weight.
Table I
Hours of brooding.
48 54 58 91 96 124 264
Absolute weight in grammes.
Increase.
Hourly percentage increment.
Percentage of water.
0-06 0-20
0- 33
1- 20
1- 30
2- 03 6-72
0-14 013 0-87 0-10 0-73 4-69
38-3 16-0 7-9
1- 7
2- 0 1-6
83 90 88 83 68 69 59
Table II
Showing the percentage of water in the human embryo up to birth. (From Davenport, after FehHng.) The the weekly percentage increments of weight. Absolute
weight in Increase, grammes. 0-98
Ago in weeks.
6 17 22 24 26 30 35 39
36-5 lOO-O 242-0 569-0 924-0 928-0 1640-0
35-52 63-5 142-0 327-0 355-0 4-0 512-0
Weekly percentage increment.
331-2 34-8 71-0 67-6 15-6 0-1 13-8
at various stages table also shows
Percentage of water.
97-5
91- 8
92- 0 89-9 86-4 83-7 82-9 74-2
fO'/,
60%
6o%
6o 70 to ;a
Days 10 iO SO *0 â– fO
Era 1 - Curve showing change in percentage of water in frog tadpoles from the first to the eighty-fourth day after hatching. Abscis^, days ; ordinates, percentages. (After Davenport, from Korschelt and Heider.)
There are other external factors by which growth may be affected- such as heat, light, and atmospheric pressure. We cannot consider these now. We may, however, profitably turn our attention for a moment to one feature which is characteristic of growth in general, of the growth of the animal orgamsm under normal conditions, and that is the change that takes place during growth in the rate of growth itself.
The rate of growth may be measured by the percentage increments of weight (or of other measurements where weight is not available) during a given interval of time ; that is to say, by expressing the increase in weight during a given period as a percentage of the weight at the beginning of that period. The change of rate, if any, is found by taking such percentage increments for successive equal increments of time.
As a first example let us consider the data furnished by Minot for the rate of growth, after birth, of guinea-pigs.
Table III
Showing tlie change of rate of growth in male and female guinea-j)igs, as measured by daily percentage increments of weight. (From Minot.)
Age in days.
Mean daily per
Age in months.
Mean daily per
centage increments.
centage increments.
i>luiiCS.
1^ em ales.
IVTa Ida
iviaieo.
emciiu!s>
0-0
2-1
Q O
0-05
0-2
4- 0
5-6
5-5
Q V
0-3
0-2
7-9
5-5
54
10
d.\J
0-1
0-1
10-12
4-7
4-7
11
0-04
0-1
13-15
5-0
5-0
12
0-1
0-05
16-18
4-1
4-3
13
-0-2
0-3
19-21
3-9
3>5
14
0-5
-0-03
22-24
3-1
1-7
15
0-2
0-00
25-27
2-8
1-9
16
0.07
0-2
28-30
2-8
2-6
17
-0-1
-0-02
31-33
1-9
1^8
18
-0-05
-0-2
34-36
1-7
1-6
19-21
0-006
-0-1
37-39
1-9
1-8
22-24
0-02
-0-05
40-50
1-2
1-1
55-65
1-3
1-3
70-80
1-2
0-8
85-95
0-9
0-9
100-110
0-7
0-8
115-125
0-6
0-5
130-140
0-1
0-2
145-155
0-4
-0-03
160-170
0-3
0-5
175-185
0-2
0-2
190-200
0-2
0^
An inspection of the accompanying table and figure (Fig. 2) will show at once that there is in both sexes almost from the moment of birth a decline in the growth-rate. The decline is not, however, uniform.
The rate falls rapidly between about the fifth day (when it is from 5% to 6%) and the fiftieth, from the fiftieth day onwards more slowly, becoming eventually very small, zero or even negative.
The younger the animal, therefore, the faster it grows ; the more developed it is the more slowly it grows. The rate of growth, in fact, diminishes as development proceeds.
This post-natal decline in the rate of growth is a continuation of a process which has been going on for some time, perhaps from the first movement at which growth began.
This may be gathered from the data given for the human embryo in Table II, and is graphically represented in the curve
For the study of the post-natal growth of man numerous data have been collected by various observers. Quetelet's measurements for boys are shown in the accompanying figure (Fig. 4). This shows that at the end of the first year after birth the percentage increment is as high as 200%, or nearly, but that then this increment drops to just over 20% at the end of the second year. From this point onwards the decline is slow but sure, until at the thirtieth year the annual percentage increase is on y 0-1%. The change of rate of growth in females is practically the same as in males.
Fig. 2.-Curve showing the daily percentage increments in weight of female guinea-pigs. (From Mmot, 1907.)
The monthly percentage increment immediately before birth is about 20% ; according to the curve (Fig. 4) this represents ra::ual ptentage increment of, -y, 250y a ^ ~ increase at the end of the first year is about 200 ^ The post natal is, therefore, a continuation of the pre-natal change.
There are, further, two points at which the rate diminishes with great rapidity : between the fourth and sixth months of pregnancy and between the first and second years after birth Elsewhere the diminution is gradual.
Fig. 3.- Curve showing monthly pre-natal percentage increments in man; (From Minot, 1907.)
A point of importance is that in both sexes there is a slight temporary rise in the growth-rate about the time of puberty Tsee the curve). This rise is always earlier in females than in males
A comparison of the growth of these two mammals is interesting.
A guinea-pig reaches 775 grammes in 432 days. ^ j^an » 63,000 grammes in 9,428 days.
The average percentage increments are
Guinea-pig 0-47 grammes.
Man 0-02
YEAPS , J 5 « 5 6 7 8 . - " 4.-Curve showing the yearly P-f -f.^^^^^ boys. (From Minot, 1907.)
In the human being, therefore, growth is mnch slower than in tie guinlpig, »d 'nran is only eventually the b.gger oi the two beeause he goe. on growing for - ™ch "ng^^
It is of course a commonplace of embryology s of all the organs of
as 'senescence . ine sai there is an increase
evidence to show that during differentiation there in the camount of cytoplasm in the cell, a decrease in the size of the nucleus, and a decrease in the rate of nuclear and cell division. It is suggested that differentiation and senescence alike depend on an increase in the cytoplasm. During segmentation,
Fig. 5. - Curves showing the alteration during the first twenty years of life of the rate of growth of stature, length of head, length of vertebi'al column, and length of leg in the human being (males). (Constructed from Quetelet's data.) Ordinatos, percentage increments ; abscissae, years.
that is, the initial process of cleavage of the fertilized ovum, before differentiation begins, the reverse of this occurs, for, as we shall see later on, the essence of segmentation probably lies in a reduction of the cytoplasmic matter relatively to the nucleus until a definite ratio between the two is attained. Then differentiation sets in.
Literature
F. Boas. The growth of Toronto children. U.S.A. Report of the Commissioner of Education, ii, 1897.
C. B. Davenfobt. The role of water in growth. Proc. Boston Soc. Nat. Hist, xxviii, 1899 (1).
J. W. Jenkinson. Experimental Embryology. Oxford, 1909.
C. S. MiNOT. Senescence and rejuvenation. Journ. Phys. xii, 1891.
_ The problem of age, growth, and death. Pop. Sci. Monthly, 1907.
A. QuETELET. Anthropometric. Bruxelles, 1870.
Note - Although in the foregoing account I have adhered to Minot's method of meSna the rate of growto by the percentage increment, I should pomt out that T TMlonTArTEnt. Melh. xxv%xvi 1908) ^as proposed to measur^^ simnlv bv the average increment per unit of time over a short mterval of I'^e ilius i we ca^ the magnitude measured, say the weight, at any ^°^'^^\^>Ji f^L^ cerUin interval^of time A* suppose the weight to have increased to x+A^, then the increment during this interval per unit of time, measures the rate. Mmot's
Ax 100
percentage increment is of course -^-j- x - •
The eranh of the gr"wth-rate constructed by Minot's method, as t^^e .^8"^^^ given abov?descends^apidly at first, more gradually later, and so presents alikeness
Jn'jffoSmLKu'm to a maxunum -d descending t^^^
has pointed out, a rate which, as the equation
^ = Mx) (A-x)
states, depends at any moment on the ^^-^,'^^^^^^17^^^^^ If xeactd.^' which has still to occur (A-x) before the end-point (^) ot^^^^^ ^^^^ Robertson suggests that gi'^^h is based on che^^^^^^^^^^ accomplished, and
^ifth1t^ETasl«^^ , It follows from the equation just cited that the velocity jis at a maxunum when
x = when the reaction is half over, and the theory that growth takes place in this
lerved (^^) with the theoretical (f ) growth-rates, and the observed with the theo °1tJi:fth\1q«^
^=Mx) (.A-x) At
^^l = k{A-x),
U will be seen whv Minot's gro wtf-Lt^curve should be similar to that of a unimolecular reaction the equation for which is
^ = UA-x).
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Jenkinson JW. Vertebrate Embryology. (1913) Oxford University Press, London.
- Vertebrate Embryology 1913: 1 Introduction | 2 Growth | 3 The Germ-Cells, their Origin and Structure | 4 The Germ- Cells, their Maturation and Fertilization | 5 Segmentation | 6 The Germinal Layers | 7 The Early Stages in the Development of the Embryo | 8 The Foetal Membranes of the Mammalia | 9 The Placenta | Figures
Cite this page: Hill, M.A. (2024, April 18) Embryology Book - Vertebrate Embryology (1913) 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Vertebrate_Embryology_(1913)_2
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
