THE BLOOD-PLATELETS 81 



negative result, and when we consider that the skin of the bat 

 is thickly pigmented, and two layers of this together with the 

 vessels have to be observed with transmitted light, it is evident 

 that the experiment is one most difficult of repetition. N. H. 

 Alcock, who has carefully examined several bats for the purpose of 

 verifying this particular statement, was quite unable to observe 

 platelets within the vessels, even under the most favourable 

 conditions of illumination, and with the use of the highest apo- 

 chromatic objectives which could be used. The proof given by 

 Bizzozero and Laker is, however, direct and positive, and without 

 making any attempt to diminish the value of their work it is most 

 desirable that this particular observation should be repeated. 

 Any stretching of the patagium must be avoided, so that the 

 vessels shall remain uninjured. The platelets are stated by 

 Bizzozero to be seen immediately this structure is examined. 



Into the further history of this somewhat acrimonious 

 controversy it would be profitless to enter. Just as it is 

 beyond any question possible to obtain films of mammalian 

 blood which do not show a single platelet, so Lowit states that 

 when the mesentery is spread out and bathed with castor oil 

 at first " besides red and white corpuscles no other morphological 

 elements are to be seen." As the observation is continued 

 platelets may appear, but never to the amount noticed when 

 physiological saline containing - 6 per cent. NaCl is employed 

 instead of oil. Possibly in the light of our present knowledge 

 the assumption that normal saline is in any sense an indifferent 

 fluid must remain uncertain, even if the percentage of salt renders 

 the fluid isotonic with that of blood plasma. 



In shed blood platelets may occur but sparingly, indeed may 

 be entirely absent. To explain this latter fact it is taught that 

 these bodies largely disappear when blood leaves the vessels. 

 To preserve them, enable them to be counted, stained, and 

 examined, a variety of methods have been devised. These 

 fixing, preservative fluids are often added in considerable 

 quantity. For example, " a drop of blood allowed to fall into 

 5 c.c. of a mixture containing # 5 per cent, osmic acid and 75 per 

 cent. NaCl " is an accepted method for their demonstration. The 

 fluids employed by Hayem, Marcano, Determann, Acquisto, 

 Afanassiew, Brodie and Russell, the last of whom tried a 

 large number of different media ranging from 33 per cent, 

 caustic potash to mixtures of alcohol, glycerine, and water, 



6 



