7-48 



NUTRITION. 



Ilaller ; but it has been generally overlooked 

 by subsequent physiologists, until attention was 

 drawn to it by the enquiries of Messrs. Addison, 

 Gulliver, and others. It is in the buff'y coat, 

 however, that the fibrous arrangement is best 

 seen ; on account, as it would appear, of the 

 stronger attraction which the particles of fibrin 

 have for one another, when its vitality has been 

 raised by the increased elaboration to which it 

 has been subjected. That there are varieties of 

 plasticity in the substance, which, on account 

 of its power of spontaneously coagulating, we 

 must still call Jibrin, appears from this fact 

 among others, that, in tuberculous subjects, 

 the quantity of fibrin in the blood is higher 

 than usual (Andral and Gavarret), although its 

 plasticity is certainly below par. It is easy to 

 understand, that its plasticity may be increased 

 as that it may be diminished ; and this either in 

 the general mass of the blood, or in a local de- 

 posit. In fact, the adhesions which are formed 

 by the consolidation of coagulable lymph, or 

 in other words, of liquor sanguinis, whose plas- 

 ticity has been heightened by the vital actions 

 of the white corpuscles in the capillaries of the 

 part on which it has been effused, often 

 acquire very considerable firmness, before any 

 vessels have penetrated them ; and this firmness 

 must depend upon that mutual attraction of the 

 particles for one another, which in up ladle de- 

 posits is altogether wanting, and which in 

 caco-plastic deposits is deficient. A very inte- 

 resting example of a structure entirely composed 

 of matted fibres, and evidently originating in 

 the simple consolidation of fibrin, has lately 

 been discovered by the writer. This is found 

 in the membrane adherent to the interior of the 

 egg-shell (membrana putaminis); and also in 

 that which forms the basis of the egg-shell itself. 

 Between the two, there is no essential difference; 

 as may be seen by examining " an egg without 

 shell," as it is commonly termed, (or rather one 

 in which the shell-membrane has been uncon- 

 solidaied by the deposition of calcareous matter); 

 or by treating the egg-shell with dilute acid, so 

 as to remove the particles of carbonate of lime, 

 which are deposited in the interstices of the net- 

 work. The place of the shell is then found to 

 be occupied by a membrane of considerable 

 firmness, closely resembling that which sur- 

 rounds the albumen of the egg, but thicker and 

 more spongy. After maceration for a few days, 

 either of these membranes may be separated 

 into a number of laminae, each of which (if suf- 

 ficiently thin) will show the beautiful arrange- 

 ment of reticulated fibres, which is delineated 

 in the accompanying figure (fg. 405). It is 

 impossible to refuse to such a structure the desig- 

 nation of an organ kal tissue, although itcontains 

 no vessels, and must be formed by the simple 

 consolidation of fibrin, poured out from thelining 

 membrane of the oviduct of the bird. It is 

 probably in the same manner, that the chorion 

 of the mammiferous animal originates; since 

 this is a new envelope, formed around the ovum, 

 during its passage along the Fallopian tube. In 

 the latter, for an ulterior purpose, vessels are 

 afterwards developed, by extension from the 

 contained ovum; and by the nutrition they 



Fig. 405. 



Membrane of egg-shell. 



supply, its size is increased, and changes take 

 place in its texture. But in the egg-membrane 

 of the bird, there is no need of vessels ; because 

 no subsequent change in its texture is required, 

 and its duration is sufficient for the purpose it 

 has to answer. 



In all these instances, the fibrillated structure 

 contains a certain amount of corpuscles, which 

 lie in the meshes of its network. These have 

 been termed " exudation-globules" by some 

 authors, by others " organic germs," and by 

 others (especially Mr. Addison) are regarded as 

 identical with the white corpuscles of the 

 blood. They may present considerable varie- 

 ties in size and appearance ; having in some 

 instances the characters of fully-formed cells, 

 whilst in others they rather resemble nuclei or 

 aggregations of granules. It seems difficult to 

 believe, that they can be identical with the white 

 corpuscles of the blood ; since if the exudation 

 has been poured forth by open orifices, suffi- 

 ciently large to admit these to pass, there would 

 be no obstacle to the escape of the red corpus- 

 cles, at least where the latter are of smaller 

 size, as in mammalia. They are probably to 

 be regarded as originating in the fibrinous de- 

 posit, from germs which it contained, when 

 effused from the vessels ; of which germs the 

 white corpuscles may have not improbably 

 been the parents. The degree of their deve- 

 lopement into cells would appear to depend 

 upon the degree of plasticity of the deposit. 

 Not unfrequently they seem arrested in their 

 progress ; especially in cases where the exuda- 

 tion verges towards a caco-plastic character. 

 In the egg-membrane, very few of these cor- 

 puscles are seen ; and as it is thus almost 

 entirely composed of consolidated fibrin, it 

 possesses considerable toughness. The same 

 is the case with highly plastic exudations from 

 inflamed serous surfaces. But in deposits 

 which are less plastic, we see a larger number of 

 these corpuscles, and a diminution and de- 

 creased tenacity of the fibres ; the membrane 

 then becomes quite friable, and approaches the 

 character of a purulent exudation. The caco- 

 plastic deposits will be presently noticed, un- 

 der the head of Abnormal States of Nutrition. 

 At present we shall proceed to consider the 

 application of these facts to the ordinary con- 

 ditions of that process. 



The question naturally suggests itself, in 

 limine, whether any of the tissues of the animal 

 body are formed by the simple effusion of fibrin 



