16 TISSUES AND ORGANS 



subject agree more or less with Arneth's deductions, although 

 they may differ from him in their definition of the essential 

 characters of a nuclear lobe. In this matter it were well to follow 

 Cooke, who contends that no nuclear part should be called a lobe 

 unless it be connected by nothing more than a single basi-chromatic 

 fibril. If this method be used as a routine many diagnostic and 

 prognostic deductions of great clinical value can be drawn from 

 microscopical examination of blood films, so that the method 

 should not be neglected, even if the theoretical inferences of 

 Arneth are disputed. It is not necessary to do more than indicate 

 that Arneth has complicated his method still further by sub- 

 dividing the various groups according to the shape of the individual 

 nuclear lobes, but this laborious technique has not found much 

 support from clinical hsematologists, perhaps because of its 

 difficulty. Certainly there is no extensive evidence of its value 

 other than the work of its discoverer, which is very profound and 

 has extended over very many years. 



Blood Platelets. There is probably no formed element of the 

 blood about which so much ink has been spilt, but the modern 

 position can be defined quite briefly. The usually accepted 

 contention is that blood platelets are derived from the megakaryo- 

 cytes of the blood marrow. These are large elements of irregular 

 shape in which there lies a large and contorted nucleus. The most 

 interesting feature of these elements is the granularity of the 

 cytoplasm. The granules are minute intensely azurophilic 

 structures which do not lie evenly distributed in the cytoplasm, 

 but are collected into small discrete grouj^s. Wright contended, 

 and most microscopists agree with him, that these fields of granules 

 with the surrounding portion of cytoplasm are projected as 

 pseudopodia through the lining of the blood vessels of the marrow, 

 then being broken off in the blood stream where they are blood 

 platelets. Wright's original pictures were indeed very suggestive, 

 but more recent observations of the occurrence of abnormal blood 

 platelets has strengthened the evidence very much. In cases of 

 hsemorrhagic purpura it is common to find gigantic forms of 

 platelets in the peripheral blood ; these are not usually simply 

 larger forms of the ordinary element, but show quite different 



