=How Beer weakens the Heart.=--Whisky was at one time thought to strengthen the heart, but doctors generally agree now that it weakens the heart. It may make the heart beat a little stronger for a few minutes, but after that the beating is weaker than usual. Much use of beer is known to make fat collect around the heart and also cause some of the heart muscle itself to change into fat. In this way the heart becomes so weak that it can no longer do its work, and death results. The reports from Germany show that hundreds of persons die every year from weakened hearts made so by the use of much beer. =Alcohol hurts the Blood Vessels.=--Careful examination of the blood vessels of drunkards after death shows that in many cases the alcohol has caused the walls of the vessels to become thick and sometimes hard. The thickening of the wall makes the channel of the tube smaller. The heart must then work much harder to get the blood through to feed the tissues. =Tobacco and the Heart.=--Many boys who use tobacco regularly do not have a steady heart beat. This is specially true of those who smoke several cigarettes daily. A few years ago, when our country was at war with Spain, thousands of young men, wanted for soldiers, were examined to find out whether their bodies were strong enough to endure the hardships of war. Hundreds were refused admittance to the army because of weak bodies, and many of them were reported by the physicians as having hearts weakened by the use of tobacco. The boys preparing for the army at the Military Academy at West Point and for sea fighting at the Naval Academy at Annapolis are not allowed to smoke cigarettes. Our country must have strong men for hard work. Tobacco never gives strength, but often causes weakness. CHAPTER XVII INSECTS AND HEALTH =Malaria or Chills and Fever.=--Malaria is a disease in which the patient usually has a chill followed by a fever at the same time each day or every other day. Thousands of people suffer from this sickness in the warm parts of our country and hundreds of them die every year. In some regions people cannot live because this sickness attacks every one who comes there. Many years ago a doctor found in the blood of malaria patients tiny animals. He thought that they might be the cause of the illness, but he could not find out how they got into the blood. =Finding out how Malaria Germs get into the Blood.=--It had been noticed for many years that mosquitoes were always found wherever there was malaria. In the year 1900 two men decided to find out if they could live in a malaria region and not have the disease when the mosquitoes were kept from biting them. [Illustration: FIG. 73.--Position of the common humpback mosquito at rest with body full of blood sucked by thrusting the bill into the flesh.]