Paper - The morphology and development of intestinal folds and villi in vertebrates
Embryology - 23 Apr 2024    Expand to Translate
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Hilton WA. The morphology and development of intestinal folds and villi in vertebrates. (1902) Amer. J. Anat. 1: 459-504.
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The Morphology and Development of Intestinal Folds and Villi in Vertebrates
By
William A. Hilton,
From the Laboratory of Hktology and Embryology, Cornell University. with 2 tables and 87 fiqure
(1902)
Draft page only
- This paper was presented to the faculty of Cornell University as a thesis for the degree of Doctor of Philosophy, May 1908. I wish to express my grateful apprecia- tion of the facilities placed a6 my disposal by the Department of Histology and Embryology, and for the aid and encouragement of the instructing staff. I am also greatly indebted to Prof. B. 0.Wilder of the Department of Vertebrate Zoology, who very kindly enabled me to .examine many valuable specimens which are in the possession of that Department.
Introduction
For many years confused ideas have been prevalent concerning the form and occurrence of mucosal folds and villi in the different divisions of vertebrates, and even yet it is not entirely clear just where folds cease and villi begin. There are great variations in occurrence even in closely related forms, but much of this confusion may be due to the various methods of study which have been employed. Compara- tively few investigators have made an extended study of the folds and villi in the different classes, although quite a number have made careful investigations of a single vertebrate class, and much work has been done upon the folds and TIilli of different species when the general digestive system of a typical form was described.
The phylogenetic study of an organ often reveals many perplexing structures which may render conclusions very doubtful. In such a study of folds and villi, difficulties present themselves which are almost insurmountable without the aid of embryology. So in order to obtain a correct idea of the primitive as well as the more advanced forms of mucosal elevations, it is necessary not only to make rather extended observations of numerous species of all great groups, but also to trace the development in several types of vertebrate embryos. The possibili- ties for work along these lines are very great, and in this investigation, only so far as time and material would allow, such work was attempted. An effort was made to determine as clearly as possible the limits of folds and villi; to describe the character of folds and villi in some forms not already dexribed as well as to supplement what was known about others; to determine, as far as possible, the form of folds and villi characteristic of different groups of vertebrates; to throw some light upon the development af villi in different forms-first, by the general survey of conditions existing in adult species; second, by em- bryological study of a few types.
Methods
In order to obtain folds and villi in their usual form, fixation must be used which will not cause the muscular fibers of the muscularis mucosle to contract and so produce unusual shapes. The intestines were usually injected and placed in the hardening fluids before the tissues had ceased to be irritable, so almost any of the fixing fluids which are rapid in their action were not desirable. Although formalin acts quickly, it was found to be very satisfactory, as the villi appeal only slightly distorted, but it was not so useful when the finer structural elements were to be preserved. Miiller’s fluid, or a solution of 3 per cent dichromate of potash, does very well for preserving villi, in that the action of these fluids is slow and villi are seldom contracted; but when these fluids are empicyed, the epithelium is usually exfoliated. At times a rather high percentage of alcohol was efficient as a preserva- tive, as the action was not rapid.
After hardening the inteztines either in the fixing fluid or in alcohol, rather thick sections were cut in collodion; the thickness of the sec- tions depending upon the size of the villi to be examined. Examina- tions of the whole intestine under liquids often helped to determine the character of folds or villi. When the muscular coats were thin enough, bits of intestine were stained with hydrochloric acid carmine, and mounted mucosa up. When this was not possible, villi were exam- ined which had been isolated by scraping or cutting from the mucosa.
For counting and measuring folds and villi, various methods were used. The most satisfactory, but not always applicable, method was by means of an ocular micrometer in squares. When villi were very numerous and the walls of the intestine thick, they were counted by removing a measured bit of mucous membrane and isolating the villi from it, counting their tips or bases until by repeated trials, uniform results were obtained. In every case the intestines were studied by as many different methods as possible and the results compared.
The following is a list of the methods ordinarily used for each specimen:
- Fixation by two or more methods.
- Naked eye examination, with isolation of villi to be studied under a lens or microscope.
- Cutting free-hand sections if possible.
- Mounting mucosa up after staining, if the muscular walls were thin enough.
- Cutting serial sections from tissues imbedded in paraffine or collodion.
For the work on embryological development of folds and villi the usual fixing and staining fluids were employed.
Character and Occurrence of Fold and Villi
Cite this page: Hill, M.A. (2024, April 23) Embryology Paper - The morphology and development of intestinal folds and villi in vertebrates. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_morphology_and_development_of_intestinal_folds_and_villi_in_vertebrates
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
