20 LABORATORY LESSONS IN GENERAL SCIENCE 



9. What effect 

 on the return of 

 blood to the heart 

 has muscular exer- 

 cise, whether work 

 or play? What in 

 the appearance of a 

 pers6n is evidence 

 of a sluggish circu- 

 lation? 



10. Why is work 

 a blessing rather 

 than a curse to 



FIG. 9. This position makes impossible the full o Whpn HOP^ 



deep breathing necessary for health. 



it become a curse? 

 INFECTION 



1. It is known that the cause of many of the diseases 

 that are "catching" is the introduction into the human body 



of living organisms so minute as to 



be seen only when examined under 



the microscope. These are very 



properly called microorganisms, or 



microbes, or simply germs. Many of 



these are minute forms of plant life 



known by the name of bacteria. Once 



lodged within the body these germs, 



under conditions favorable to their 



growth, will multiply in number at a truly marvelous rate, 



and directly or indirectly bring about a diseased condition in 



the patient. What is the meaning of the term bacteriology ? 



FIG. 10. Size of bacteria 

 relative to that of the 

 point of a fine needle, 

 both greatly magnified. 



