330 ANNUAL REPORT OF THE Off. Doc. 



body that becomes dry, produces living creatures. He also asserted 

 that animals are formed in putrefying soil. A true conception of 

 the wonderful changes of form which insects undergo was unknown 

 before the year 1618. Prior to that time insects were supposed to 

 have been spontaneously generated. Eels were supposed to be gen- 

 erated from the slime of the Nile and maggots were thought to be 

 spontaneously generated in meat. Dr. Francesco Redi, physician 

 to the Grand Dukes Ferdinand the Second and Cosmos the Third 

 of Tuscany, made an interesting series of experiments aod proved 

 that maggots never develop in meat if flies are prevented from 

 laying their eggs on it. He showed that the maggots were the 

 young of the flies and that the maggots hatched from eggs laid by 

 the flies, and destroyed the belief in spontaneous generation for all 

 time. The wonderful changes in form in insects is well illustrated 

 by the butterfly, the female of which lays a minute egg on a plant; 

 the egg hatches and produces a little caterpillar which feeds on the 

 plant until full grown; it then changes into an immovable apparently 

 dead object, termed a chrysalis. In due time a butterfly emerges 

 from the chrysalis and the same process is repeated through the 

 seasons indefinitely. It is oecessarj^ to understand these life his- 

 tories to get a rational idea of insect life in relation to economic 

 entomology. 



Before we can understand the transmission of disease by insects 

 it is uecessar}^ to know something of the new science knowu as bac- 

 teriology, and popularly known as the germ theory of disease. It 

 is, however, no longer a theory but a demonstrated scientific truth. 

 In 1862 the celebrated French scientist, Pasteur, proved that many 

 floating particles in the air were living, organized bodies. These 

 are popularly called germs. Pasteur also proved that a«imal solids 

 did not putrefy or decompose if kept free from access of germs. In 

 187;>, Obermeier observed minute, actively moving, flexible, spiral 

 organisms in the blood of patients suffering from relapsing fever. 

 These discoveries were followed by equally important ones, demon- 

 strating the cause of consumption, cholera, plague and other dis- 

 eases. Thus many disease's are caused by minute living organisms, 

 which are in some cases vegetable a«d some animal. The vegeta- 

 ble organisms are called bacteria and are minute plants. They can 

 only be seen under the higher powers of the microscope. The unit 

 of measurement for bacteria is one micro-millimeter, which is equal 

 to one twenty-five thousandth of an inch. They are found every- 

 where except in the atmosphere of high mountains. Thev mav enter 

 the human body by means of the digestive tract, the respiratory 

 tract, and the skin and mucous membranes if abraded, punctured 

 or broken. Most of the species of bacteria are harmless, some bene- 

 ficial and a few are dangerous and cause many of the ills to which 



