Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25760/20/
12 
DIGESTION. 
of these is a large membranous bag, analogous 
to the paunch of the ruminants, into which the 
food, without any previous alteration, is re¬ 
ceived from the oesophagus, and where it is 
macerated in the usual manner by the conjoined 
action of heat and moisture. 
The gizzard is of much smaller dimensions 
than the crop, composed of four muscles, two 
of which are of a flattened form and of very 
dense texture, lined internally with a firm cal¬ 
lous membrane, and capable of an extremely 
powerful action. These constitute the main 
part of the parietes, the two other muscles being 
much smaller, and situated at the extremities, 
serving, as it would appear, merely to com¬ 
plete the cavity* The gizzard is so connected 
with the crop, that the food, after due macera¬ 
tion, is allowed to pass by small successive 
portions between the two larger muscles ; by 
their contraction they are moved laterally and 
obliquely upon each other, so that whatever is 
placed between them is completely triturated. 
The force of these muscles, as well as the 
impenetrability of their investing membrane, is 
almost inconceivably great, so that, according 
to the experiments of Spallanzani and others, 
not only are the hardest kinds of seeds and 
grains reduced to a perfect pulp, but even 
pieces of glass, sharp metallic instruments, 
and mineral substances, are broken down or 
flattened, while the part still remains unin¬ 
jured .f The action of both the crop and the 
gizzard must be regarded as at least essentially 
mechanical, mainly adapted for the purposes 
of maceration and trituration, and as compen¬ 
sating for the saliva and teeth of man and the 
greatest part of the mammalia. We are able 
in this case to observe the connexion between 
the habits of the animals and the peculiarities 
of their organs more clearly than with regard 
to the ruminants, for we can always perceive 
an intimate relation between the food of the 
different kinds of birds and the structure of 
their stomach. 
II. An account of thenatureof the substances 
usually employed as food.—All the articles that 
are employed in diet may be arranged under 
the two primary divisions of animal and vege¬ 
table, according to the source whence they are 
derived. Those in which the distinctive cha¬ 
racters are the most strongly marked differ both 
in their proximate principles and their ultimate 
elements, although in this, as in most other cases, 
there are many intermediate shades. The ulti¬ 
mate elements of vegetables are oxygen, hy¬ 
drogen, and carbon, to which, in some cases, 
a portion of nitrogen is added. Animal sub¬ 
stances contain all these four ingredients, the 
carbon being in less quantity than in vege¬ 
* Grew, ubi supra, p. 34; Blumenbach, ubi 
supra, <$99: Peyer, Anat. Ventr. Gall., in Man- 
eet, Bibl. Anat. t. i. p. 172; Hunter on the Ani¬ 
mal (Economy, p. 198-9; Clift, in Phil, 'frans, for 
1807, pi. 5, fig. 1 ; Home’s Lect. v. n. pi. 49, 02 ; 
and the art. AVES. . Q , ,n 09 . 
t Spallanzani, Dissert, x. § 5 .. 8, and 10. . 22 , 
see also Acad, del Cimento, p.268,9; Borelli, De 
motu anim. t. ii. prop. 189; Redi, Espenense, p. 89 
et seq. ; Grew, ch. 8 ; the art. “ Birds in Rees ; 
and “ Aves” by Mr. Owen, in the present work. 
tables, while the hydrogen, and still more the 
nitrogen, are generally in much greater quan¬ 
tity. There are various circumstances which 
seem to prove that either species of diet is 
alone competent to the support of life, although 
each of them is more especially adapted to 
certain classes of animals. This, it is pro¬ 
bable, depends both upon the chemical and 
the mechanical nature of the substances in 
question, but perhaps more upon the latter 
than the former, for we find that the processes 
of cookery, which act principally upon mecha¬ 
nical principles, render various substances per¬ 
fectly digestible, which the stomach could not 
act upon before they had undergone these 
operations. We also find that animals, which, 
in their natural state, have the strongest in¬ 
stinctive predilection for certain kinds of food, 
may, by a gradual training and the necessary 
preparation of the articles employed, have their 
habits entirely changed, without their health 
being in any degree affected. 
There is, however, a circumstance in the 
structure of the animal, which clearly points 
out a natural provision for the reception of one 
species of food in preference to the other, viz. 
the comparative capacity of the digestive or¬ 
gans. It may be concluded that, in all cases, 
the aliment must undergo a certain change 
before it can serve for the purpose of nutrition, 
and that this change will occupy a greater 
length of time, and that a greater bulk of 
materials will be requisite, according as the 
nature of the food received into the stomach is 
more or less different from the substance into 
which it is to be afterwards reduced. Hence, 
as a very general rule, we find that the diges¬ 
tive organs of carnivorous animals are less 
capacious than those of the herbivorous, and 
that even in the latter there is a considerable 
difference, according as the food consists of 
seeds and fruits or of the leaves and stems of 
plants. 
There are indeed certain circumstances in the 
habits of some of the carnivora which require 
organs of considerable capacity, as, for ex¬ 
ample, those beasts of prey who take their 
food at long intervals, being supplied, as it 
were, in an occasional or incidental manner, 
so that it becomes necessary for them to lay up 
a considerable store of materials, and to take 
advantage of any opportunity which presents 
itself of replenishing the stomach. The anato¬ 
mical structure of the human digestive organs 
indicates that man was intended by nature for 
a mixed diet of animal and vegetable aliment, 
but with a preponderance towards the latter ;* 
and it appears in fact that, while a suitable 
combination of the two seems the most condu¬ 
cive to his health, and to the due performance 
of all his functions, either species is alone 
competent to his growth and nutrition.j~ 
* Cuvier, Règne Animal, t. i. p. 86; Lawrence’s 
Lect. p. 217 et seq. ; see also the elaborate dis¬ 
sertation of Richter, De victus animalis antiq. &c. 
f Haller, El. Phys. xix. 3. 2 . . 4 ; these sections 
contain a very full account of the different kinds of 
diet employed by different nations or individuals. 
We have a number of curious facts of this kind in