306 Major Ronald Boss [March 2, 



Prof. Ray Lankester suggests for the blasts of the Heemamoebidae the 

 simple term " filiform young." 



At this point the investigations took a tarn of extreme interest 

 and importance, scarcely second even to what attached to the first 

 study of the zygotes. Since the blasts are evidently the progeny of 

 the zygotes, they must carry on the life-history of the parasites to a 

 further stage. How do they do so ? What is their function ? Do 

 they escape from the mosquito, and in some manner, direct or in- 

 direct, set up infection in healthy men and birds ? Or, if not, what 

 other purpose do they subserve ? It was evident that our knowledge 

 of the mode of infection in malarial fever — and perhaps even the 

 prevention of the disease — depended on a reply to these questions. 



As I have said, the zygotes become ripe and rupture about a week 

 after the insect was first infected — scattering the blasts into the body- 

 cavity of the host. What happens next ? It was next seen that by 

 some process, apparently owing to the circulation of the insect's 

 body- fluids (for the blasts themselves appear to be almost without 

 movement), these little bodies find their way into every part of the 

 mosquito — into the juices of its head, thorax, and even legs. Beyond 

 this it was difficult to go. All theory— at least all theory which I 

 felt I could depend upon — had been long left behind, and I could 

 rely only on direct observation. Gnat after gnat was sacrificed in 

 the attempt to follow these bodies. At last, while examining the 

 head and thorax of one insect, I found a large gland consisting of a 

 central duct surrounded by large grape-like cells. My astonishment 

 was great when I found that many of these cells were closely packed 

 with the blasts — (which I may add are not in the least like any 

 normal structures in the mosquito). Now I did not know at that 

 time what this gland is. It was speedily found, however, to be a 

 large racemose gland consisting of six lobes, three lying in each side 

 of the insect's neck. The ducts of the lobes finally unite in a common 

 channel which runs along the under surface of the head and enters the 

 middle stylet, or lancet, of the insect's proboscis. 



It was impossible to avoid the obvious conclusion. Observation 

 after observation always showed that the blasts collect within the 

 cells of this gland. It is the salivary or poison gland of the insect, 

 similar to the salivary gland found in many insects, the function 

 of which, in the gnat, had already been discovered — although I 

 was not aware of the fact. That function is to secrete the fluid which 

 is injected by the insect when it punctures the skin — the fluid which 

 causes the well-known irritation of the puncture, and which is pro- 

 bably meaut to prevent either the contraction of the torn capillaries 

 or the coagulation of the ingested blood. The position of the blasts 

 in the cells of this gland could have only one interpretation — 

 wonderful as that interpretation is. The blasts must evidently pass 

 down the ducts of the salivary gland into the wound made by the 

 proboscis of the insect, and thus causes infection in a fresh vertebrate 

 host. 



