LOUSE FEEDING EXPERIMENTS 43 



2. RESULTS OF THE LOUSE FEEDING EXPERIMENTS 



The results and important data of the louse feeding exper- 

 iments are tabulated in Table VIII. 



The answer to the first question awaiting solution "the 

 determination of the nature of the demonstrable micro-organ- 

 isms acquired by lice nurtured upon typhus patients" was 

 clean cut Rickettsia prowazeki. The occasional finding of 

 this micro-organism in a series of largely negative experiments 

 in the first part of our work led to changes, mentioned above, 

 in temperature of incubator, duration of the daily feedings and 

 duration of the whole period of feeding; after the changes were 

 made, lice in experimental boxes were almost always infected 

 with this micro-organism. 



In the fifty-two experiments, Rickettsia prowazeki appeared 

 in the lice of twenty-seven. With the recognition of the con- 

 ditions favorable for infection of the lice, we were able to secure 

 almost uniformly positive results. Rickettsia appeared in lice 

 in each of the last thirteen consecutive feeding experiments and 

 in eighteen out of the last twenty-one consecutive experiments 

 following the longer feedings and raising of the incubator tem- 

 perature to 30 C. The identification of the rickettsia as 

 Rickettsia prowazeki was in each instance based upon appear- 

 ances seen in serial sections of lice; although the incidence of 

 infected lice in each box was largely determined by smear 

 preparations. 



In lice from six boxes we found a few infected with an ex- 

 tracellular rickettsia (Figs. 32 and 64, plates ix and xxvi), 

 which, from its distribution, deep staining and morphology we 

 believe to be Rickettsia pediculi. 



In some lice there was a double infection with intra and ex- 

 tracellular rickettsia (Fig. 64, plate xxvi). The source of this 

 infection with Rickettsia pediculi can with considerable con- 

 stancy be traced to three of several patients upon whom five 

 of these boxes were fed (Boxes XLVII, L, LI, LIII, LIV, Experi- 

 ments 35, 38, 39, 41, 42). The symptoms in each patient were 

 those of typhus; nothing in the history or in the clinical course 



