The present state of knowledge concerning the causation of shock having been thus briefly reviewed, the question of the treatment of the condition may be discussed. In this connexion the value of blood transfusion will be considered. It will have become clear that essentially the condition to be combated in treating shock is one of lowered blood pressure following upon a diminution of the volume of blood in the circulation. All the factors which have been mentioned in considering the causation of shock must be combated. Warmth must be supplied, morphia administered, fractures efficiently immobilized, damaged tissues excised: but clearly all these measures are prophylactic rather than curative. None of them will remove a state of profound shock once established, for they will not of themselves restore the blood volume depleted by capillary stasis. It is necessary, therefore, to attack this condition directly. It may with justice be compared to a state of acute anæmia following hæmorrhage, but with this difference, that the blood is still present in the body and will return to the circulation when the capillary stasis has been abolished and the circulating balance has been restored. The possibility of recovery from shock depends upon how long the condition has existed. After a certain time the toxæmia, whether the primary traumatic toxæmia or the secondary increase in hydrogen-ion concentration, appears to have a damaging effect upon the capillary walls, so that an increased loss of fluid takes place into the tissues and this cannot be remedied. It is essential, therefore, to use the means which will most rapidly restore the circulation and bring about a rise in blood pressure which will be permanent. It is reasonable to infer that the most hopeful means of bringing this about is by a blood transfusion, which will actually replace the blood temporarily lost. This is the physiological remedy, and its value has been proved by the results obtained in many cases of my own as well as in those recorded by others. The efficiency of the treatment is accentuated by the fact that so large a proportion of cases of shock are associated with, and aggravated by, some degree of hæmorrhage. Apart from this, Keith’s observations have shown that the diminution of blood volume in shock is comparable with that which attends severe hæmorrhage. The state of shock in fact so closely resembles hæmorrhage that most of the same remarks concerning blood volume and the amounts that should be given by transfusion may be applied, and it is unnecessary to repeat them here. It must be remembered, however, that in pure shock the amount of hæmoglobin in the body is not reduced though there is less in the circulation. It is restored to the circulation when the capillary stagnation is overcome. This will be referred to again later on.