44 BLOOD PLATELETS. [BOOK i. 



their disappearance as being a ' destruction ' or ' dissolution.' We 

 have as yet no exact knowledge to guide us in this matter, but 

 we can readily imagine that, upon the death of the corpuscle, the 

 substances composing it, after undergoing changes, are dissolved 

 by and become part of the plasma. If so, the corpuscles as they 

 die must repeatedly influence the composition and nature of the 

 plasma. 



But if they thus affect the plasma in their death, it is even 

 more probable that they influence it during their life. Being 

 alive they must be continually taking in and giving out. As we 

 have already said they are known to ingest, after the fashion of 

 an amoeba, solid particles of various kinds such as fat or carmine, 

 present in the plasma, and probably digest such of these particles 

 as are nutritious. But if they ingest these solid matters they 

 probably also carry out the easier task of ingesting dissolved 

 matters. If however they thus take in, they must also give out ; 

 and thus by the removal on the one hand of various substances 

 from the plasma, and by the addition on the other hand of other 

 substances to the plasma, they must be continually influencing the 

 plasma. We have already said that the white corpuscles in shed 

 blood as they die are supposed to play an important part in the 

 clotting of blood ; similarly they may during their whole life be 

 engaged in carrying out changes in the proteids of the plasma 

 which do not lead to clotting, but which prepare the proteids for 

 their various uses in the body. 



Pathological facts afford support to this view. The disease 

 called leucocythaemia (or leukaemia) is characterised by an increase 

 of the white corpuscles, both absolute and relative to the red 

 corpuscles, the increase, due to an augmented production or 

 possibly to a retarded destruction, being at times so great as to 

 give the blood a pinkish grey appearance, like that of blood mixed 

 with pus. We accordingly find that in this disease the plasma is 

 in many ways profoundly affected and fails to nourish the tissues. 

 As a further illustration of the possible actions of the white 

 corpuscles we may state that, in certain diseases in which minute 

 organisms, such as bacteria, make their appearance in the blood 

 and tissues, white corpuscles may attack and devour these bacteria, 

 thus acting as " phagocytes," and in this way, or otherwise, by 

 exerting some influence on the bacteria or the products of their 

 activity, modify the course of the disease of which the bacteria are 

 the essential cause. 



Blood Platelets. 



33. In a drop of blood examined with care immediately 

 after removal, may be seen a number of exceedingly small bodies 

 (2 fj, to 3 fL in diameter) frequently disc-shaped but sometimes of a 

 rounded or irregular form, homogeneous in appearance when quite 



