COLOURLESS CORPUSCLES OF BLOOD. 133 



may be reasonably regarded as the means, by which the requisite change is 

 effected. Exactly the same may be said of the Albuminous matter contained 

 in the Yolk of the Egg, which is certainly not in a condition in which it can 

 be immediately applied to the purposes of nutrition ; and its conversion may 

 be regarded as commencing with the development of transitory cells within 

 its own substance, and as being completed by means of the cells forming the 

 inner layer of the germinal membrane, by which it is subsequently taken up 

 and introduced into the current of blood flowing through the vascular area 

 ( 149). A similar purpose is probably answered by the transitory cells de- 

 veloped within the germinal vesicle ; and by those which appear at a similar 

 period, in the evolution of the descendants of the " twin cells" produced in 

 it. Many similar examples have been elsewhere adduced. 



o. There are probably cases, however, in which cells are very rapidly called into exist- 

 ence, without that preparatory elaboration of their nutrient materials, which we regard as 

 due to the vital operations of a preceding generation. Thus the Bovista giganteum, a large 

 fungus of the Puff-ball tribe, has been known to increase, in a single night, from a mere point 

 to the size of a huge gourd, estimated to contain 47,000,000,000 cellules. In such a case it 

 is difficult to suppose mat any but the most rapid mode of generating cells can have been in 

 operation ; and the idea that these could not have been developed by any such elaborate 

 process as that just alluded to, is borne out by the fact of their extremely transitory charac- 

 ter, the decay of such a structure being almost as rapid as its production. The same may be 

 remarked of those fungous growths in the Animal body, which sprout forth most rapidly. 

 Hence the apparent exception assists in proving the rule. 



154. We have thus a class of facts, which indicates that the conversion of 

 the Chemical compound into the organizable principle the aplastic into the 

 plastic material is effected, in the particular situations where it is most 

 wanted, by the vital agency of transitory cell-life ; that is, by the production 

 of cells, which are not themselves destined to form an integral part of any 

 permanent structure, but which, after attaining a 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 purpose in particular situa- 

 tions, 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 therefore an adapt- 

 ation of the circulating fluid to the wants of the whole fabric. 



155. It is not in the Blood alone, that floating cells are met with; for Cells, 

 which seem identical with the Colourless corpuscles of the blood, are found 

 in the Chyle and Lymph fluids in which, as in the Blood, the elaboration 

 of plastic Fibrine from unorganizable Albumen is continually taking place, to 

 make up for the constant withdrawal of the former substance by the nutrient 

 processes. Hence there would seem reason for attributing this important 

 function to these floating cells; the number of which present in the fluids, 

 seems to bear a very close relation with the energy of the elaborating process. 

 It is a fact of great physiological interest and importance, that, whilst the 

 colourless corpuscles are to be met with in the nutritious fluids of all Animals 

 which possess a distinct circulation, the red corpuscles are nearly restricted to 

 the blood of Vertebrata. This observation, which was first put forth by 

 Wagner,* has been confirmed by the Author, who had been previously struck 

 with the very close analogy between tbe floating cells carried along in the 



* [Elements of Physiology, translated by R. Willis.] 

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