232 Transactions. — Miscellaneous. 



parasites to be found in the blood on which the mosquitos 

 had fed. This proved definitely that these pigmented cells 

 were developed from the malarial parasite. 



Light was thrown on the way in which the process of 

 development occurs by an American observer, McCallum. 

 He showed in another bird parasite that the purpose of the 

 flagella was to fertilise others of the parasite which did not 

 form flagella. The flagella entered into these and mixed 

 with their substance, which underwent certain changes, as a 

 result of which the form altered into a somewhat conical 

 body endued with power of locomotion and penetration. If 

 the vermicule met with a blood-corpuscle it apparently bored 

 right through it. These stages of development have since 

 been shown actually to occur in connection with the malarial 

 parasite of man, and it has been shown that it is a vermicular 

 form which is able to penetrate the wall of the mosquito's 

 stomach and there developes into these sac-like bodies. 



Eoss, then, had traced the malarial parasite of birds as far 

 as the stomach-wall of the mosquito. His next observation 

 was that some of the mosquitos, after several days, had 

 scattered through them minute rod-like bodies. On pressing 

 on some of the larger of the sac-like bodies, and thus causing 

 their rupture, he found that innumerable rods of the same 

 kind were liberated, and he concluded, therefore, that the 

 bodies ruptured naturally, and their contents, these rods, were 

 so liberated into the circulation of the mosquito. This the 

 anatomy of an insect would readily permit. Ross showed it 

 was so by pricking the back of a mosquito and examining the 

 minute drop of blood thus obtained. It abounded in the rod- 

 like bodies. In endeavouring to determine the function of 

 these rods Ross came across a gland connected with the pro- 

 boscis of the mosquito, in which the rods seem specially to 

 collect ; and not only did he find them in the gland, which was 

 the salivary gland of the insect, but also in its duct, which 

 opens through the proboscis. This salivary gland forms a 

 fluid which is injected into the skin of the animal on which 

 the mosquito feeds before it begins to suck. It is supposed 

 that this saliva keeps the blood from clotting, and so aids the 

 mosquito in getting a good meal. At all events, it was pro- 

 bable that when a mosquito containing these rods attacked an 

 animal some of the rods were injected at the site of puncture. 

 Ross accordingly allowed mosquitos which had had time to 

 develope these rods to bite sparrows. These in due course 

 developed malaria. Thus was established the proof that 

 mosquitos play the part of an intermediary host for the mala- 

 rial parasites of birds — in other words, that the mosquito 

 carried the infection from bird to bird. 



Ross published his discoveries at once, and forthwith many 



