54 Causes of Disease. 



phuretted hydrogen (in poisoning from the gas of manure pits) 

 acts partly by paralyzing the nervous system, partly by forming 

 sulphmethaemoglobin, giving a greenish (almost cadaveric) tint to 

 the blood. Hydrocyanic acid and cyanide of potassium also cause 

 a rapid paralysis of the central nervous system, in addition to 

 interfering with oxygenation of the blood cells and tissues (cyan- 

 methaemoglobin, bitter-almond odor in the organs). Potassium 

 chlorate, nitrobenzole, potassium nitrate and amyl nitrite cause 

 marked destruction of red corpuscles and transform haemoglobin 

 into methsemoglobin, in which the oxygen is more firmly fixed 

 than in the oxyhgemoglobin. The blood, and of the organs in such 

 instances the kidneys especially, take on a striking brown color. 

 Extensive hsemocytolysis, with liberation and solution of the 

 haemoglobin in the blood plasma, giving a blood-red color 

 to the urine (haemoglobinuria), are caused by various toxines 

 of fungous and bacterial origin (ptallin, helvellic acid), arsenu- 

 retted hydrogen, anilin, nitrous acid (fumes), carbolic acid and 

 other poisons. Coagulation of the blood and its sequels are seen 

 in poisoning with ricin (from the seeds of castor oil plant) and 

 abrin (from the seeds of abnis precatorius). 



Infectious Agencies. 



By the term infection (inficere, to put into, to inoculate, 

 to taint) is meant the entrance into the system of a disease-pro- 

 ducing microorganism capable of self-multiplication, a pathogenic 

 microbe. 



Nature is richly supplied with microorganisms ; which on the 

 borders between the animal and vegetable kingdoms represent 

 primitive forms of living matter, in their minuteness are visible 

 only with the aid of the microscope and are recognizable as 

 consisting of but single cells. According to their classification 

 as plants or animals, they are spoken of as protophytes or pro- 

 tozoa. There are forms which are only visible with a magnifica- 

 tion of 2,000 diameters, and even then as barely perceptible points 

 without definable cellular characters ; and there are reasons for 

 believing that still smaller organisms exist, invisible with our 

 present optical instruments, but by no means unreal, being dem- 

 onstrated as corpuscular entities by other methods, as by their 

 detention in filtration or by inoculation (so-called invisible 

 microbes). 



