THE CONSERVATION OF LIFE 



239 



taneously with the drop of saliva which the Anopheles lets flow 

 into the wound which it bores with its proboscis, numerous 

 gymnospores. Here the germs probably invade at once the red 

 blood corpuscles direct observations are as yet absent develop 

 into mononts, and these divide again into spores. With this act 

 infection is complete and the cycle may commence anew. A 

 fever fit announces the presence of malaria. 



The reproduction-cycle of the malaria parasite represents a 

 change of generations, that is, a change and a regular succession 

 of sexual and asexual reproduction. We shall hear of similar 

 cases among the metazoans in the next lecture. 



Though all this sounds very simple it required an enormous 

 amount of labour before the life-habit of the parasite had been 

 accurately determined, for it must be clear to every one that the 

 disentangling of the threads entailed much more than merely to 

 observe under the microscope the 

 blood of a malaria fever patient, 

 the contents of his intestines, and 

 the salivary gland of a mosquito. 

 But man does not penetrate 

 Nature's secrets quite so easily. 

 Perhaps it was only chance which 

 first indicated in the blood of a 

 malaria patient one or another 

 stage of the parasite. This dis- 

 covery is followed up, the blood 

 of healthy and infected persons 

 is examined, and it is found that 

 only the latter contains similar 

 germs. Gradually the conclu- 

 sion is arrived at that these 

 minute organisms stand in some relation to the sickness. One 

 searches for the way by which the parasites can have reached 

 the human blood. There are so many possibilities. The most 

 diverse hypotheses are constructed, examined, and rejected until 

 finally the right way is found and the carrier discovered in blood- 

 sucking insects : in this particular case, the Anopheles. 



Again, in the interior of the Anopheles are found parasites 

 of very different appearance, gymnospores, amphionts, oocytes, 



FIG. 58. THE MA.LARIA MOSQUITO 



(Anopheles clavig&r) . 



