380 



PSYCHE. 



disease is a blood-parasite, and that it is 

 propagated by the cattle tick. The 

 germs sucked in with the blood of 

 diseased cattle reach the eggs of the 

 tick, and the new generation of ticks, 

 developed from the infected eggs, con- 

 vey the Texas fever to the sound cattle 

 upon which they are ajjplied. His 

 experiments were repeated and con- 

 firmed in Eastern Africa by Koch, who 

 In view of the relations which seem to 

 connect the presence of mosquitoes 

 with the transmissibility of malaria, 

 does not hesitate to make those insects 

 responsible for the propagation of the 

 malaria infection. He does not think, 

 however, that the latter can be commu- 

 nicated by so simple a process as that 

 of a mosquito first stinging a malaria 

 patient and afterward a sound person, 

 such as I have, in my theory, considered 

 capable of causing the transmission of 

 yellow fever. The grounds for this 

 distinction, however, are not very ap- 

 parent. In the case of the tick, which 

 is supposed not to attack a second ani- 

 mal after parting from its first host, the 

 exclusive transmission by the second 

 generation, infected through the eggs, 

 may be considered a necessity ; but it 

 is otherwise with mosquitoes, at any 

 rate with those which I have observed 

 in Havana. After an interval of two 

 or more days, which they require to 

 digest the blood and empty themselves, 

 they are ready to sting the next victim 

 that ofl'ers, and may do so as many as 

 ten or twelve times, during the thirty 

 or more days that I have been able to 

 keep them alive. It is, therefore, quite 



admissible that, when the mosquito be- 

 comes contaminated, not only its eggs 

 but also its salivarv and venom glands 

 may be iavaded by the jjathogenous 

 germs, so that the latter may be dis- 

 charged with the secretion of those 

 glands along tlie track of the wound and 

 into the capillary vessel entered by the 

 sting when the insect attacks its next 

 victim. Indeed, on some rare occa- 

 sions I have seen mosquitoes die within 

 twenty-four hours after they had stung 

 a patient with severe yellow fever, 

 without assignable cause, for they still 

 retained some of the blood which they 

 had sucked ; whence it might be sur- 

 mised that the yellow-fever germ is 

 pathogenic for the Havana mosquitoes, 

 though the infection seldom proves 

 fatal for those insects. 



In August last, during my stay in the 

 field hospitals on the hills near Santi- 

 ago, I witnessed a fact which, as far as 

 it went, agreed with my theory about 

 yellow fever, inasmuch as there were 

 neither mosquitoes, mosquito eggs, nor 

 larvae to be found in my encampments, 

 and not a single case of yellow fever 

 occurred among the one hundred and 

 fifty men who came under ni}' observa- 

 tion, notwithstanding the daily com- 

 munications with the city. It was 

 otherwise, however in legard to mala- 

 ria, for this constituted the prevalent 

 cause of sickness in all those camps. It 

 assumed various types : the quotidian 

 or tertian intermittent, the remittent, 

 irregular, or subcontinuous ; but in 

 most of the cases it was accompanied 

 by diarrhoea (sometimes mixed with 



