MEDICINE, RECENT ADVANCES IN. 



bottle-. He caused the mosquitoes thus reared to ach wall pigmented bodies exactly similar to those 

 s ati'ected with malaria, and then dis- which he had found in his rare species of mos- 



*tctfd the mosquitoes for evidence of the develop- quito, fed on the blood of a man with malaria. 

 of the parasite within them. The first result These pigmented bodies grew rapidly, and soon 



formed protrusions, like warts, on the walls of the 

 stomach. When he dissected one of these mature 

 warts he found it full of minute, rod-like bodies, 

 which he called germinal rods. Soon after the 

 warts had filled up w r ith the germinal rods he saw 

 them burst open and scatter the" rods into the 

 general body cavity of the mosquito outside of 

 the stomach. For a considerable time, although 

 he watched very closely, he got no further. But 

 one day, in dissecting the head of a mosquito, he 

 came upon the final link in the chain. 



One could hardly suggest an investigation that 

 would seem to be more barren of practical utility 

 than the dissection of a mosquito, and yet in the 

 hands of Dr. Ross it led to the final and complete 

 solution of the malaria problem. He found, on 



of these experiments apparently disproved the 

 theory, for he failed to obtain a mosquito whose 

 bite would cause the disease. Not only this, but 

 he traced the malaria germ into the mosquito's 

 stomach, and found that it died there. He so 

 thoroughly believed in the guilt of the mosquito, 

 however, that he persevered, varying his experi- 

 ments in all sorts of ways, and dissecting, in two 

 years, more than 1,000 mosquitoes. Up to this 

 time he had employed only two kinds of mos- 

 quito, but one day in August, 1897, a native 

 brought him a bottle of larvae from an unknown 

 source, and when he raised these he found that 

 they produced a new kind of mosquito. He in- 

 duced the new mosquitoes to bite a malaria pa- 

 tient ; and in two of them, when they were dis- 



sected, round bodies, possessing the typical ma- dissecting the head, two glands, the ducts from 



laria pigment, were found in the walls of the 

 stomach, and here at last was the long-sought 

 extra-corporeal phase of the parasite. He watched 

 these bodies, and found that they grew very rap- 

 idly, increasing from ten to twelve times in di- 

 ameter. 



At about this time Dr. W. G. MacCullum, of 

 Johns Hopkins University, announced a discov- 



which united and ran to the root of the pro- 

 boscis. These proved to be the salivary glands, 

 and in and around them he found great numbers 

 of the germinal rods. If these same processes 

 could be demonstrated in the mosquito for the 

 human malaria germ, the mosquito cycle was 

 proved and the etiology of the disease completed. 

 In a very short time this was done, not only by 



ery regarding the development of a somewhat the Italian students Grassi, Celli, Bignami, and 



i j i j _ j_i J.T i >,<;.,,,.. n : 1,,,* ^ i ,-, ^ i^ff ~r\ T/'.^^'U 4-i A /^i rt . 



similar protozoal parasite in the pigeon, the im- 

 portance of which, in connection with the extra- 



Bastianelli, but also by Dr. Koch, the German pa- 

 thologist, and the case was completed from the 



corporeal phase of the malaria germ, Dr. Manson laboratory point of view. It was found that 



immediately perceived. Dr. MacCullum had found - -_ *- 1-*~ .~ i- : .- - 



that the arms of the flagellated body of the 

 pigeon parasite were not simply spores, as had 

 been believed, but were really sexual bodies which 

 required for their further development a female 

 cell. Ross was in constant communication with 

 Dr. Manson, and was soon informed of MacCul- 

 lum's discovery. His work was now unavoidably 

 interrupted, and when he was able to resume it, 

 .early in 1898, could not, owing to the plague scare 



Ross's failure to complete the cycle in man was 

 due to his not having had, except in one instance, 

 above referred to, the proper variety of mosquito 

 to work with. This proved to be the Anopheles. 

 The common gray or brindled mosquito which 

 abounds in all mosquito-haunted localities be- 

 longs to a group known as Culex, which, fortu- 

 nately, is not hospitable, for some unknown rea- 

 son, to the malaria germ. That is, the latter will 

 not grow in the stomach of the Culex into the 

 spindle-like germinal rods that seem 

 to be necessary for completing the 

 cycle. 



This cycle in the Anopheles mos- 

 quito, as worked out by the Italians 

 for the tropical form of the disease, 

 which is illustrated on pages 346, 

 347, is as follows: When malaria- 

 infected blood enters the stomach of 

 the mosquito the malaria parasites 

 develop into two different bodies. 

 One is a spherical protoplasmic mass, 

 and the other the flagellated body. 

 These originally were the crescent 

 bodies. The long arms of the flag- 

 ellated body soon break away from 

 the central mass, and each one final- 

 ly enters one of the spherical bodies 

 and coils up in it. This combined 

 form soon develops the ability to* 

 move about, and eventually forces 

 its way into the substance of the 

 stomach wall. Here it becomes motionless and be- 

 gins to grow rapidly, so that in a few days it pro- 

 trudes from the stomach wall like a wart. At this 

 parasite time it is filled with thousands of the small spin- 

 >een observed in cer- die-like germinal rods. This wart-like excrescence 

 >me of the Calcutta soon ruptures, and discharges its contents of ger- 



THE CHANGES THAT OCCUR IN THE ^ESTIVO-AUTUMNAL PARASITE AFTER 

 IT HAS BEEN DRAWN INTO THE MOSQUITO'S STOMACH. 



No. 4 is the flagellated body. No. 5 shows three of the flagella 

 i-hich have broken loose from 4, and one of which is seen entering the 

 female sarnetocyte in 6. This combined form finally enters the stom- 

 ach wall of the mosquito, and its growth produces the wart-like appear- 

 ance shown on page 347. (After Koss.) 



in Calcutta, where he was now stationed, secure 

 satisfactory human experimental material. He 

 was very anxious to go on with the work, and so 

 turned his attention to a malaria-like parasite 

 (proteosoma) which had 

 tain birds. He collected 



I j - - * *-* pi/Hi COj OtUU U-lO^liCtl tiCO 1 L-O ^^ill/CHL'O VJ. fe^* 



ws, and found that many of them contained minal rods into the body cavity outside of the 



is gcnn which lived m the red blood-corpuscles, stomach. The rods immediately disappear into 



e malaria germ lives m human blood, the tissues of the mosquito, and are soon found in 



He pastured a herd of uninfected mosquitoes on - L1 -~ - 1 " --'- -*L_:._ 



some of these infected sparrows, and after a few 

 days dissected the former. He found in the stom- 



countless numbers in its salivary glands; and 

 some of them gain entrance into every person the 

 mosquito bites. 



