Such is the almost invariable result in middle-aged and elderly persons; in the young, however, the chances of recovery are much more favorable. Salter[22] states "that in youth the tendency is invariably toward recovery, whereas in one attacked with it after forty-five the tendency is generally toward a progressive severity of the disease and the production and aggravation of those complications by which asthma kills." The favorable result in childhood he attributes to the recuperative power of youth: growth and change, being more rapid than later in life, enable the system to repair during the intervals whatever damage may have been sustained during the paroxysms. [Footnote 22: _On Asthma_, Am. ed., p. 168.] There is another class of cases in which, owing to our being able to recognize and remove the cause, the prognosis is quite favorable: thus, if it has been discovered that the disease is due to some local influence, change will often effect a cure, and the patient will remain well as long as he remains in the locality which agrees with him, but generally relapses if he ventures to return to the place where he first contracted the disease. The same may be said of that form of asthma in which the disease is due to some trade or pursuit necessitating the inhalation of irritating dust or gases: the indications are obvious. Cases in which the paroxysms have been traced to the presence of nasal polypi or to a tumor pressing upon the course of the pneumogastric nerve have been promptly cured by the removal of these growths. In all these cases it is presupposed that there is no organic disease, for the presence of any one of the serious complications we have mentioned would dissipate all hope of cure. In arriving at a prognosis it is all-important to inquire into the severity and frequency of the attacks, as violent paroxysms at short intervals soon lead to incurable complications. It is also essential to ascertain the condition of the patient during the intervals between the paroxysms: if at that time he feels well and does not suffer with shortness of breath, we may infer that as yet no organic change has occurred; if, however, he complains of more or less dyspnoea during the intervals, we may safely conclude that some organic disease has set in and that the case is incurable. Salter attaches great importance to the persistence of expectoration during the intermissions, regarding it as indicative of bronchitis, and therefore as an unfavorable indication: to use his own words, "Spitting is one of the worst signs in asthma."