490 SCIENCE PROGRESS 



of malaria by mosquitoes the life-cycle of the parasite was 

 being studied eagerly in all parts of the world, they will 

 recollect that almost every writer on the subject at that time 

 invented a new terminology of his own for the various stages 

 of the parasite. It is somewhat late in the day to add another 

 system of nomenclature to the many already consigned to 

 oblivion and that put forward by Ross labours under the 

 further disadvantage of attempting to found a general ter- 

 minology upon the intricacies of a special case, instead of 

 employing terms long in use and founded on a wider out- 

 look, in order to adapt them to the special requirements of 

 those occupied with a limited range of objects. 



The malarial theorem, as Ross aptly terms it, may be stated 

 briefly as follows. Malaria in man or animals is a disease 

 caused by a minute parasite which lives and multiplies in the 

 blood, passing its trophic phase within the red blood-corpuscles. 

 The parasite is propagated from one vertebrate host to another 

 by the agency of certain mosquitoes, which, on sucking 

 the blood of an infected vertebrate, take various stages of 

 the parasite into their stomachs with the blood ; one stage of the 

 parasite resists the action of the digestive juices of the mosquito 

 and passes through a sexual process of generation and multi- 

 plication within the body of the mosquito, the cycle ending 

 after some days with the production of many thousands of 

 minute germs (" protospores," Ross) lodged in the salivary 

 glands. If the mosquito then succeeds in biting a vertebrate 

 of the right kind, that is to say, of the kind which is a specific 

 host of the parasite in question, the germs pass down its 

 proboscis and are inoculated into the blood, thus bringing 

 about a fresh infection of the disease. Every statement made 

 in the foregoing sentences is based on rigorous experiment or 

 accurate microscopical investigation. It only remains to add 

 that the various species of malarial parasites are specific to 

 certain hosts, vertebrate or insect ; those of birds, for instance, 

 can only be transmitted by mosquitoes of the subfamily Culicinae ; 

 those of men only by the subfamily Anophelinae. 



The principles of malarial prevention depend on the facts 

 stated above; their aim is to interrupt the complex chain of 

 circumstances upon which the existence of the parasite depends. 

 If the parasite cannot pass from man into the mosquito, or 

 from the mosquito into man, it becomes extinct with the death 



