40 TUBERCULOSIS 



The Bacillus. The specific causal agent of tuberculosis is a rod- 

 like organism whose length varies from one-fourth to one-half the 

 diameter of a red blood corpuscle (1.23 to 4.12 of a micron). It is 

 slender and non-motile. It was formerly believed that this, like other 

 bacteria, should be classed among microscopic plants, but the most 

 exact chemical studies have failed to show the presence of cellulose in 

 their structure. This organism does not take the ordinary basic 

 aniline stains readily, but when treated with certain stains, such as 

 carbol-fuchsin, and heated, it stains deeply and retains the color even 

 after washing with dilute mineral acid. For this reason it is known 

 as an acid-fast bacillus and it has been found that this group contains 

 a number of micro-organisms whose relationship has been a matter of 

 great interest. By special staining, tubercle bacilli are easily detected 

 in sputum and other excretions from tubercular lesions. 



There is still some discussion whether or not this bacillus forms 

 spores. The low temperature at which it is destroyed and the fact 

 that it is speedily killed by sunlight renders spore formation highly 

 improbable. In old cultures, branched forms are occasionally seen. 

 The tubercle bacillus contains large amounts of fat and wax and it is 

 probable that these protect this organism from the destructive action of 

 the secretions of the body cells. It has been a parasite for so long that 

 it has developed this method of protecting itself. It grows slowly both 

 on artificial media and in the animal body. It is not its purpose 

 to kill its host but to feed on him as long as possible. Unaided it 

 seldom does kill, but the necrotic tissue caused by its growth forms a 

 suitable medium for the lodgment and growth of other bacteria and 

 tuberculosis usually terminates as the result of a mixed infection. So 

 long as the infection is unmixed, the progress of the disease is slow. 

 As a rule, there is no sputum until the infection becomes a mixed one ; 

 consequently when one waits for a diagnosis of this disease until the 

 bacilli are found in the sputum, he waits too long. The physician of 

 thirty years ago believed tuberculosis an incurable disease, because at 

 that time he could not make a diagnosis until there was a troublesome 

 cough with much expectoration, marked emaciation and a long-con- 

 tinued hectic fever. All patients that reached this stage died. After 

 Koch's discovery of the bacillus, diagnosis had to await the detection 

 of this organism in the sputum. Again, it was too late. With 



