THE GRASSHOPPER 351 



of the interior of the human or animal body, begin to develop. This is 

 the common way in which typhoid fever is carried, for one can hardly 

 get this disease unless some excreted matter from a typhoid patient has 

 been eaten in this way. 



An excellent way to demonstrate the fact of insects' eggs being 

 almost everywhere on our foodstuff is to take any fruit, such as a banana, 

 apple, cherry, or grape, and place this in a bottle plugged with cotton, 

 so that air may pass in but nothing else can. In a short time various 

 forms of animal life will be found therein. As these forms of life hatched 

 from eggs, the eggs must have been on the fruit before it was placed in 

 the bottle. It is of value to note that even after one has washed the 

 fruit well, such hatching will almost always occur, showing how thor- 

 oughly these insects fasten their eggs either on or into the surface struc- 

 tures of these fruits. 



When different kinds of crops are planted different kinds of insects 

 will thrive, as those alone will survive which have a sufficient food sup- 

 ply. Those not feeding on the new plants either leave for satisfactory 

 fields, or die. If it is remembered that a duck, which feeds on fish, tastes 

 totally different from one not so fed, which shows that the food of an 

 animal makes a great chemical difference to the body tissues, it can 

 be understood how different diseases may come forth when parasites 

 change their food and environment. For, if it makes a chemical differ- 

 ence in the flesh of an animal as to what it eats, it means also that if a 

 new chemical substance in a parasite is poisonous to man, then the same 

 parasite when feeding on one food may not be poisonous and not cause 

 disease, whereas when feeding on another type of food, such chemical 

 poison may cause disease. Then there is the interesting fact that many 

 diseases of birds will not affect a frog normally when such disease germs 

 are injected, but, if the frog be placed in an incubator where its blood 

 becomes of the same temperature as that of the bird from which the 

 disease is taken, the disease will develop. This illustrates how different 

 temperatures change the susceptibility of different organisms to differ- 

 ent diseases. 



The animals commonly called grasshoppers are really of varying 

 types (Fig. 229), the true grasshopper being long-horned; that is, it has 

 two antennae as long or longer than its entire body. The family to 

 which these belong is known as Locustidae, while the short-horned 

 grasshoppers belong to the family Acridiidae. 



In America the Rocky Mountain Locust is the one which does the 

 great damage to crops. The exact time of laying and hatching of eggs 

 varies somewhat with the region of the country. 



Often the young, until after the second or third moult, content 

 themselves with feeding on whatever food is close at hand, but as soon 

 as this food becomes scarce the animals congregate and "in solid bodies, 

 sometimes as much as a mile wide, march across the country, devouring 



