rsvciiE. 



881 



blood). This instance, at any rate, 

 shows that Kocli's assertion, that 

 '■ where there are no mosquitoes there 

 is no mahiria,'" is altogether too abso- 

 Inte. In those camps, 1 believe the 

 propagation must have been ellected 

 tlirough the flies (of which there was a 

 great abundance). These insects, in 

 spite of all precautions, had ample 

 opportunities of picking up, from the 

 discharges of the malaria patients, not 

 only the malaria parasites contained in 

 the extravas.ited blood, but also some 

 infectious intestinal germ, with both ot 

 which organisms the\' may have con- 

 taminated the U)od and beverages used 

 bv the men wlm subsequently showed 

 >igns of the double iiifeclion. A \cl- 

 low-fever epidemic occurring uniler sim- 

 ilar circumstances, in the absence of 

 )-ello\v- fever mosc[uitoes, might nr)t be 

 so readily reconciled witli mv thcnrv 

 about tliat disease, which is tounded 

 upon more definite and more exclusive 

 arguments than those recorded in c(m- 

 ncction with the malaria infection. 

 The following instance may serve to 

 illustrate my meaning In the capital 

 of Mexico, and in other districts of 

 similar altitude above the sea level, 

 Mexicans who nevei- have visited the 

 lowlands have no immunity whatsoever 

 against yellow fever, a sure proof that 

 no epidemics of that disease ever occur 

 in that part of the country. It some- 

 times happen, however, that a resident 

 of the c;ipital tal;es the infectiwn by 

 gomg to Vera Cruz, though the dis- 

 ease may not declare itself until his 

 return to the capital. In such cases, 



the yellow fever will nm its usual 

 course, with the same symptoms and 

 prognosis as if the patient had remained 

 at Vera Cruz ; with this difference only : 

 that in Vera Cruz other susceptible 

 persons might readily have caught the 

 infection from him, whereas in Mexico 

 the disease is never propagated. It the 

 infection could be transmitted through 

 contact with the patient or his secre- 

 tions, l>v inhaling his emanations in the 

 sick room, or by the use of contam- 

 inated food or beverages, there would 

 be no imaginable reason why the dis- 

 ease shonlil not be transmitted at Mex- 

 ico as well as at Vera Cniz. .Such 

 not being the case, we must inter: first, 

 that a fictor wliich is necessaiv for the 

 transmission is present at Vera Cruz, 

 but is absent fiom Mexicf); and second, 

 from the circumstance of the disease 

 not being transmissible through the 

 forms of exposiu'e enumerated abo\'e, 

 that the yellow-fever germ is patho- 

 genous only when introduced in a less 

 trivial manner, probably by inoculation 

 under the epidermis or even directly 

 into a blood-vessel. Hence m}- theorj' 

 of the mosquito. 



Ni'tv Mosquito Theory. — My orig- 

 inal mosquito theory, however, in view 

 of the facts brought to light by Dr. T. 

 H. Smith, in his admirable demonstra- 

 tion of the transmission of the Texas 

 fever through the agency of the cattle 

 tick, requires siow to be somewhat 

 modified, so as to include the important 

 circmr.stance that the faculty of trans- 

 mitting the yellow-fevergerm need not 

 be limited to the parent insect, directly 



