662 
Diseases that never co-exist. 
Some very interesting results have been obtained by Professor 
Rokitansky on the incompatibility of certain diseases with each 
other. From the earliest ages a vague idea has prevailed that 
two diseases could not co-exist in the system. This opinion was 
thus far modified bv John Hunter, who says that “ no two ac- 
tions from two different morbid poisons can go on together at 
the same time in the same part or the same constitution.” Later 
observations, while they have shewn this statement, as expressing 
a general law, to be erroneous, have at the same time indicated 
that certain diseases exert upon others an opposing influence, in 
the way of the one arresting the course, in modifying the nature, 
of the other. For example, measles arid small-pox have been ob- 
served to suspend or modify the course of each other. Hoop- 
ing-cough sometimes suspends the small-pox, measles, and scarlet 
fever. Hooping-cough is frequently cured by vaccination ; it is 
sometimes also cured by small-;)OX and measles. Vaccinia may 
suspend, or in its turn be suspended by, scarlatina. The plague 
was arrested by the prevalence of small-pox, but broke out again 
on its disappearance, according to Baron Larrev. 
But these and other isolated facts were never of a sufficiently 
definite character to attract much attention ; and it remained for 
Professor Rokitansky, whose unequalled opportunities of obser- 
vation and whose acknowledged accuracy create the most per- 
fect confidence in his investigations, to put this matter wholly in 
a new light, by establishing, from an amount of cases that ren- 
ders fallacy in the result almost impossible, that certain diseases 
never co-exist ; as the presence of the one arrests the progress, or 
prevents the occurrence, of the other. The typhus abdominalis 
(that is, with formation of the characteristic typhous matter, and 
which by Rokitansky is always understood under the name of 
typhus) is excluded by the various forms of puerperal fever. In 
two hundred dissections of puerperal fever he did not find one 
complication of the typhous process. This immunity from typhus 
is given by the pregnant state, childbed, and even, though in a 
less degree, by suckling. 
Typhus and cholera, and typhus and dysentery, are said to have 
the power of mutual exclusion ; and the co-existence of tubercu- 
lous disease and typhus is extremely rare. Carcinoma and tu- 
berculosis (i. e., tuberculous disease) are antagonist diseases; 
and the latter, and all kinds of serous cysts, are never met with 
simultaneously in the same organ, or even in the same individual. 
Tubercular disease affords an immunity from cholera, dysentery, 
