386 PROCESSES OP LIFE REVEALED BY THE MICROSCOPE. 



inan. How perfectly the word "offspring' 1 describes the life process in 

 the production of this new being ! That the child should resemble both 

 father and mother is thus made intelligible, for it is a part of both. 

 Yes, further, it may resemble grandfather or great grandfather or 

 mother, for truly it is a part of them, their life conserved and contin- 

 ued. There is no new life, it is only a continuation of the old. "Omne 

 vivum ex vivo," all life from life. But the demonstration of this prime 

 fact required a microscope, and it is an achievement of the last half of 

 this century. How counter this statement still is to the common belief 

 of mankind we may perhaps better appreciate if we recall our own 

 youth, and remember with what absolute confidence we expected the 

 stray horsehairs we had collected and placed in water to turn into 

 living snakes. 1 The belief that it is an everyday occurrence for living 

 beings to arise from lifeless matter was not by any means confined to 

 those uneducated in biology. It was held by many scientific men 

 within the memory of most of us. Indeed this goblin of spontaneous 

 generation, even for the scientific world, has been laid low so recently 

 that the smoke of battle has scarcely yet cleared from the horizon. 



In the complex body of animals, as stated above, the constituent 

 elements perform different functions. Is there any hint of the way in 

 which the action is accomplished? Let us glance at two systems, the 

 nervous and the glandular, widely different in structure and function. 

 All know how constantly the glands are called into requisition, the 

 salivary glands for saliva, those of the stomach and the pancreas for 

 their digestive juices, etc. If we take now the pancreas as an example, 

 and that of a living, fasting animal is put under the microscope so that 

 its constituent cells can be observed, it will be seen that they are 

 clouded, their outlines and that of their nuclei being vague and indis- 

 tinct. The cell is apparently full of coarse grains. If now the animal 

 is fed, as the digestion proceeds the pancreas pours out its juice. At 

 the same time the granules, and with them the cloudiness, gradually 

 disappear, the cells become clear, and both they and their nuclei are 

 sharply outlined. That is, the substance which is to form the pancre- 

 atic juice is stored in the cells in the form of granules during the 

 periods of rest, and held until the digestive agent is demanded, and 

 if the demand is great all the granules may be used up. But as 

 soon as the demand ceases the cells begin again their special vital 



Reference is here made to the neruatoid worm Gordius. This worm lives a part 

 of its life as a parasite in the larva} of aquatic insects and in some fish. In the adult 

 free condition it differs markedly from the larval, parasitic stage, and is very slender 

 and much elongated, often reaching a length of 20 to 30 centimeters (8 to 10 inches), 

 and has the general appearance of a coarse hair like that from the tail of a horse. It 

 lives in water and in wet places, and frequently appears in horse troughs and the 

 wet places where the trough overflows. From the hair-like appearance it was and 

 still is believed that a hair from the horse's tail or mane had directly transformed 

 into a living creature. By many persons it is called a hair snake, by others a hair 

 worm. Often one or several become tangled in an almost inextricable knot, whence 

 the name from the famous "Gordian knot." 



