COMMUNICABLE DISEASES 383 



upon filling itself with blood of a malarial patient in whom the asexual 

 cycle has been completed. Should the mosquito bite the human earlier, 

 that is, before the gametes are matured, it would not become a transmitter 

 of malaria for obvious reasons. In the sexual or mosquito cycle, the 

 gametocytes derived from the human undergo the preliminary change 

 in the stomach of the insect (flagellation and exflagellation of the 

 male gametocyte and the macrogamete formation of the female gameto- 

 cyte). The products of exflagellation constitute the male gametes or 

 microgametes which now fertilize the macrogametes, giving rise to the 

 ookinetes. The oogonites now pass through the wall of the stomach 

 and attach themselves to or lie adjacent to the outer lining of the stomach, 

 where they grow to large size forming cysts in which are developed hun- 

 dreds of tiny spindle shaped nucleated bodies known as the sporozoites, 

 which enter the body cavity of the mosquito from which they gradually 

 are gathered into the salivary glands, where they remain until some of 

 them may be injected with the saliva into the human body, where the 

 asexual cycle again repeats itself. 



Malaria could be made to disappear from the face of the earth by doing 

 the following. 



1. Destroy all malaria bearing mosquitos, or, 



2. Destroy all humans, or, 



3. Do away with the breeding places of malaria bearing mosquitos 

 occurring within the zones of dissemination for humans, comprising 

 what is commonly known as malarial control. 



Since the malaria lorganism cannot survive unless it is provided with 

 the two hosts, namely man and mosquito, it is evident that the discon- 

 tinuance of one or the other of the two hosts, would cause the malaria 

 to disappear. Proposition (i) is practically impossible and proposition 

 (2) is not to be thought of. Proposition (3) is practicable as has been dem- 

 onstrated on numerous occasions. It is reasonable to suppose that if 

 all breedmg places of the malaria spreading mosquitos occurring within 

 the reach of humans should be rendered uninhabitable for the mosquito 

 larva, for a period sufficiently long to make sure that all latent carriers 

 were also dead, then the disease would be eradicated from the face of 



the earth. . 



Malarial control is a very definite phase of sanitary science and those 

 who are interested should consult the following special treatise. Herms, 

 William B —Malaria: Cause and Control. The Mac MUlian Company. 



F Diphtheria.— This dread disease is both infectious and contagious. 

 The primary cause is the BacUlus diphtheria, also known as the Klebs- 

 Loeffler bacillus. The chief predisposing causes are exposure to wet and 

 cold The disease may be localized in the larynx (membranous croup)- 



