NUTRITION. 
| the production of cells which are not them- 
_ selves destined to form an integral part of any 
__ permanent structure, but which, after attaining 
_ certain maturity, reproduce themselves and 
| disappear, successive generations thus following 
one another until the object is accomplished, 
after which they altogether vanish. We shall 
now consider another class of facts which seem 
to indicate that a change of this kind is being 
_ continually effected in the nutritious fluids of 
_ animals during their circulation through the 
: body, by cells which are either carried about 
_ with them, or which are developed for the pur- 
_ pose in particular situations, as in plants. The 
_ former is the more common occurrence ; since 
the conditions of animal life, usually involving 
a general movement of the body, require also a 
_ constant general reparation of its parts, and an 
adaptation of the circulating fluid therefore to 
the wants of the whole fabric. 
In the chyle drawn from the lacteals near 
the intestinal tube, there is but little fibrin; and 
_ very few of the peculiar chyle-corpuscles are 
seen in the fluid. In the chyle of the mesen- 
_ teric glands, on the other kand, the corpuscles 
are extremely numerous; and they are always 
_ readily seen in the chyle of the central lac- 
 teals, receptaculum chyli, and thoracic duct,— 
“though their number is considerably less than 
in chyle drawn by pricking the lacteals of the 
“Mesenteric glands. The average size of these 
corpuscles is about ,4,th of an inch ; but they 
vary from about 44,th to ,31th. The smallest 
are usually found in the peripheral lacteals; 
largest in the thoracic duct. They are 
evidently ced/s in process of developement ; and 
from the appearances presented by those which 
” are seen in the chyle of the thoracic duct, there 
tan be little doubt that they have the power of 
ucing themselves in the ordinary mode. 
first appearance of these cells in large 
_ Dumber is exactly coincident with the first 
| appearance of fibrin in the chyle,—at least to 
an amount sufficient to produce spontaneous 
_ Coagulation; and the delay of the chyle in the 
mesenteric glands appears to aid in their deve- 
lopement, and to assist their operation. In the 
lower Vertebrata the absorbent system has none 
these (so called) glands; and hence we see 
‘that they are not essential to the performance of 
its functions. But in such animals the vessels 
‘are immensely extended in length; whilst in 
the warm-blooded Vertebrata, in whose con- 
formation the principle of concentration ope- 
‘Tates to the greatest possible extent, we see no 
such prolongation ; the end being answered by 
_ the excessive convolution of the absorbents in 
_ the mesenteric glands, where it seems probable 
“ the chyle is delayed during the develope- 
- ment of its characteristic cells. . Similar state- 
‘ments apply to the /ymph, and to the lymphatic 
vessels and glands. This fluid is probably to 
be regarded, not as a product of the decompo- 
Sition of the tissues, which is destined to be 
thrown out of the system, but as the product 
/ 4 that secondary digestion, by which a portion 
of the materials that have formed a component 
) 7 of the tissues, and have been set free by 
eit disintegration, is again rendered subser- 
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745 
vient to nutrition, and reconveyed into the 
current of the circulation. Into the arguments 
in favour of this view (which differs from the 
ordinary doctrine regarding the function of 
the lymphatic system) we cannot here enter ; 
but it may be remarked that the animal matter 
of the lymph is mainly of an albuminous cha- 
racter, and that it gradually undergoes a trans- 
formation into fibrin during its passage through 
the absorbent vessels and glands. 
The continuation of this process in the blood 
is believed by the writer to be effected by 
means of the white, or colourless, corpuscles, 
to which increased attention has lately been 
directed. That these are identical with, or are 
the immediate offspring of, the corpuscles of 
the chyle and lymph, there seems much reason 
to believe from their similarity in size and ap- 
pearance. Whilst the red corpuscles vary in 
dimension from less than y)5;th of an inch 
(Musk Deer) to 3},th (Proteus), the colourless 
corpuscles have not been observed to depart 
widely from the diameter of s,{,th of an inch in 
any vertebrated animal; consequently, while 
they are but little larger than the average of red 
corpuscles in man, and are scarcely distinguish- 
able from them, except by the practised micro- 
scopist, they are far more minute than the oval 
blood-dises of reptiles and fishes, and are at 
once recognised, even by a cursory observer, 
Now it is a fact of great physiological interest 
and importance, that whilst the colourless cor- 
puscles are to be met with in the nutritious 
fluids of all animals, which possess a distinct 
circulation, the red corpuscles are restricted to 
the blood of Vertebrata. This observation, 
which was first put forth by Wagner,* has been 
confirmed by the writer of this article, who 
had been previously struck with the very close 
analogy between the floating cells carried along 
in the current of the circulation in some of the 
very transparent aquatic larvee, (especially thosé 
of the Culicide,) and the lymph-corpuscles of 
the Frog. Now it is evident from this fact, 
that, as the blood of Vertebrata is distinguished 
from their chyle solely by the presence of red 
corpuscles in the former, and by their absence 
in the latter, the nutritious fluid of invertebrated 
animals is rather analogous (as Wagner has 
remarked) to the chyle and lymph, than to the 
blood of Vertebrata. Or, to put the same idea 
in another form, the presence of the colourless 
corpuscles in the nutritious fluids appears to 
be the most general fact in regard to its cha- 
racter throughout the whole animal scale; 
whilst the presence of red corpuscles in that 
fluid is limited to the vertebrated classes. 
Hence it would not be wrong to infer that the 
Junction of the colourless corpuscles must be 
of a general character, and intimately connected 
with the nutritious properties of the circulating 
fluid ; whilst the function of the red corpuscles 
must be of a limited character, being only re- 
quired in one division of the animal kingdom. 
Further, it has been noticed by Mr. Gulliver 
that in the very young embryo of the Mam- 
malia, the white globules are nearly as nume- 
* Physiology, by Willis, Part II. 
