Chap. I.] INTRODUCTORY. 



sent it is only known as the product of life. The protoplasm, 

 moreover, is not distributed throughout the body in a con- 

 tinuous uninterrupted mass, but is disposed in separate indi- 

 vidual particles called cells. If you scrape gently the inside 

 of your lower lip with a pen-knife, you will remove some of 

 the cells of that part of the body. Mounted in a little saliva, 

 and examined under the microscope, 1 they will be seen (Fig. 

 24, ii.) to be flattened plates of irregular shape, sometimes 

 curled up at the edges, and containing a rounded spot at the 

 centre, called the nucleus. Of such nucleated cells (or their 

 products), differing in form and appearance in different parts, 

 the whole body is compounded. 



Is there anything further to be added ? It may be suggested 

 that animals move about and are guided by feelings. Now, 

 with regard to the feelings, it will be well to leave them on one 

 side. Each of us knows a great deal about his own feelings, 

 and very little of the feelings of his neighbours. Our know- 

 ledge of the feelings of animals is only arrived at by a complex 

 process of inference ; and with regard to the lowest animals we 

 are completely ignorant whether they have feelings or not. 

 Leaving the feelings on one side, therefore, we may notice that 

 moving about is only a particular and conspicuous manifesta- 

 tion of that general activity or vital energy which is character- 

 istic of the animal organism. A large proportion of .this activity 

 arises from the fact that the organism is eminentl^ sensitive 

 using this term not as necessarily implying feeling, but in the 

 same sense as a photographer would use the word when speak- 

 ing of a sensitive plate. The animal is sensitive in its prompt 

 and ready response and reaction to the stimulus of surrounding 

 conditions, just as a sensitive plate promptly reacts under the 



1 The student must provide himself with a good working compound micro- 

 scope. The instrument I am in the habit of recommending to my students in 

 the University College, Bristol, is a stand on the Hartnach model, with a No. 2 

 or 3 Zeiss ocular, and Zeiss' objectives A and E, or a " 1-inch" and "th-inch" 

 of English make. The former is spoken of in this book as low power, the latter 

 as high power. Such an instrument may be obtained from any first-class 

 instrument maker. The student is warned against purchasing low-priced 

 second-hand instruments by inferior makers. 



