464 Messrs. W. Cramer, A. H. Drew, and J. C. Mottram. 



The changes in the number of the platelets are given in fig. 5, p. 463. 

 A profound thrombopenia develops as a result of the exposure to radium. 

 This persists for a considerable time after the exposure to radium has ceased. 

 It is followed by a rapid spontaneous recovery to the normal number — and 

 sometimes exceeding it — within a week, if the dose of radium has not been 

 too large, as in the present experiment. With larger exposures an anaemia 

 develops and the animals die from intercurrent infections. These findings 

 have an important clinical bearing upon the cases of pernicious anaemia which 

 have occurred among radium workers and which have on a few occasions 

 resulted in death. In all these cases there has been some more or less 

 definite evidence of an infection of the blood stream which has made some 

 hesitate to attribute the condition entirely to exposure to radium. These 

 experiments probably indicate the particular part which micro-organisms 

 play in the manifestation of this type of anaemia ; and they indicate the 

 desirability of examining the platelet content in all cases of pernicious anaemia 

 especially of the aplastic varieties. 



The Function of Blood Platelets in the Mechanism of Resistance to Bacterial 



Infection. 



The observations recorded in this paper demonstrate a striking relationship 

 hetween the resistance of an animal to certain bacterial infections and the 

 number of platelets present in the blood. When these latter are diminished 

 below a certain level and kept there for some time, either by withholding the 

 fat soluble vitamin or by exposure to radium, infective conditions develop. 

 When a number of rats are kept in the same cage and on the same vitamin 

 A-free diet, only those animals develop infections in which the platelets have 

 fallen below the critical level. Those rats in which, for reasons given in the 

 paper, the platelets have not been affected to the same extent do not develop 

 these infections. When the deficient vitamin is supplied again the infective 

 conditions clear up as the number of platelets increase, provided of course 

 that these infections have not been allowed to persist for too long a time 

 producing secondary changes such as anaemia, to which the animal eventually 

 succumbs. The infections are as a rule of an avirulent kind. In one case a 

 bacteriological examination was made. Blood cultures from the heart blood 

 showed the presence of two different gram-positive bacilli belonging to the 

 diphtheroid group. 



These facts demonstrate that the platelets fulfil an important function in 

 the mechanism of resistance to certain bacterial infections. This conclusion 

 links the observations recorded in this paper to the phenomenon described 

 previously as " defence rupture " or " kataphylaxia " by one of us in conjune- 



