90 SCIENCE PROGRESS 



which have been published as to the numbers of the platelets 

 in disease must be received with even greater caution than 

 that which we are accustomed to give to the enumeration of 

 white or red corpuscles. From experimental evidence it is 

 beyond question that under pathological conditions blood- 

 platelets may exist in circulating blood ; some of these bodies, 

 such as those which are seen in cases of poisoning by phenyl- 

 hydrazine or toluylenediamine, are probably derivates from 

 the red corpuscles since they possess haemoglobin. Even 

 in shed blood similar bodies are produced, for the process of 

 separation can be witnessed. But no observations on shed blood 

 can decide this question whether " Blutplattchen," whatever their 

 nature or origin, are normal constituents of the blood. While 

 not denying the value of the evidence which has been adduced in 

 favour of their independent existence, we are unable to wholly 

 accept the view that they are cells of equal morphological 

 importance to the red and white corpuscles. We can find no 

 information which gives even a clue to their actual number 

 in circulating blood ; and since we are familiar with the exceed- 

 ingly rapid changes which blood-plasma exhibits when it leaves 

 the vessels, and also realise that no cells which we can examine, 

 not even nerve cells nor those of muscle, undergo quite so rapid 

 a change, we are justified in regarding the plasma as peculiarly 

 susceptible of damage both when within and outside the body. 

 And when damaged in a variety of ways, the change, whatever 

 may be the chemical or physical explanation of the process, 

 becomes one which can be actually observed. From all our 

 observations on the behaviour of human blood when treated 

 outside the body with the various fixing or so-called indifferent 

 fluids, we can draw no other conclusion but that the vast 

 majority, if not all, of the bodies which have been regarded 

 as platelets are, as far as histological evidence is of any 

 value, probably of the nature of plasma-separations. It is 

 admittedly difficult to prove a negative, but on the question as 

 to whether the platelets are genuine constituents of normal 

 blood we must for the present be content to suspend our judg- 

 ment. The evidence as to pre-existent haemic cells other than 

 those of the leucocytes and erythrocytes is, at the present time, 

 inconclusive. 



