In the first place Friedmann’s remedy is not a “serum.” Anti-toxins, such as those used against diphtheria and lock-jaw are sera. An antitoxin is the serum of an animal which has been treated with toxin-forming germs till his blood serum is full of defensive substances against that toxin. An antitoxin, as its name indicates, is an antidote to a poison. Friedmann’s tuberculin belongs to the class which we have of late begun to call vaccines, a term formerly applied only to the virus of cowpox but now made to cover all forms of virus which are used to stimulate the production of defensive substances. The real difference between an antitoxin and a vaccine is that the first contains an antidote and is an emergency remedy for an acute disease, while the second is a weak form of virus which causes the body of the patient to manufacture its own antidote. What Friedmann claims as novel in his tuberculin is that it consists of living tubercle bacilli, while those in general use consist of dead bacilli or their extractives. It has long been known that living bacilli would call forth a more rapid production of defensive substances than dead. Dr. Trudeau of Saranac Lake demonstrated this twenty years ago, experimenting on rabbits with bacilli of bird tuberculosis. Later several Americans confirmed his results, using non-virulent strains of human tubercle bacilli. Von Behring’s famous experiments on immunizing calves were made with living bacilli. So far therefore as is yet known, there is nothing new in the principle Friedmann is following. As to the details of his cure, we are in ignorance. It will be long before any dependable word can be given out as to the results of Friedmann’s work in New York city. Every physician knows that optimism, eagerness to grasp at every hopeful sign, are characteristics of a fair majority of consumptives. We shall need a much longer period of observation before we can be sure that this tuberculin has any superiority to the many previously tested, almost all of which have had initial success followed by more or less disillusionment. Still greater caution must be used in estimating the immunizing properties of Friedmann’s tuberculin. Friedmann treated over 300 children eighteen months ago and states that during this interval none of them have developed tuberculosis. It will be at least fifteen years before positive statements can be made concerning these children and then only by comparing them with a similar group of non-treated children living in conditions as nearly as possible identical with those of the treated children.