THE BLOOD. 29 



of mammalia., as the rodents or the ruminants, there is also 

 an obvious relation between the size of the corpuscle and that 

 of the animal. 



Gerber states that there is an exact relation between the 

 size of the blood globules and that of the smallest capillaries. 

 This observation is doubtless strictly correct. 



Structure. Much diversity of opinion has, until recently, 

 prevailed, and does still obtain, although to a less extent, in 

 reference to the intimate structure of the red globule. This 

 diversity has arisen partly from the imperfections of the 

 earlier microscopic instruments employed in the investigation, 

 and in part is due to the different circumstances in which 

 observers have examined the blood corpuscle. Thus, one 

 micrographer would make his observations upon it in one 

 fluid, and another in some other medium, opposite results 

 and conclusions not unfrequently being the results of such 

 uncertain proceedings. These discrepancies it will be the 

 writer's endeavour, as far as possible, to reconcile with each 

 other, as well as to point out those observations which are 

 entitled to our implicit belief, and those which yet require 

 confirmation. This being done, we shall be in a position to 

 form some certain conclusions. The earlier microscopic 

 observers believed, almost without exception, in the existence 

 of a nucleus in the centre of each blood corpuscle. Into this 

 belief they were no doubt led more from analogy than 

 from actual observation. Now analogy, although frequently 

 useful in the elucidation of obscure points, affords in the 

 present instance but negative and uncertain evidence. In 

 the elliptical blood discs of reptiles, birds, and fishes, a solid 

 granular nucleus does undoubtedly exist ; but the best optical 

 instruments, in the hands of the most skilful recent inicro- 



sidered to be the smallest. The following are the dimensions given by Mr. 

 Gulliver of some of the animals above named. Diameter of corpuscle of 

 the elephant, the -^-fas of an inch ; of capybara, the -g-^Ve- ; of goat, the 

 ^-gVs-5 and of napu musk-deer ^3-^5. The white corpuscles of the musk- 

 deer are as large as those of a man ; a proof that the red corpuscles are 

 not formed, as many suppose, out of the colourless blood globules. (See 

 the figs.) 



