SEX PRESELECTION THEN AND NOW: THE MOST RECENT PROPOSALS FOR SEX PRESELECTION
One of the most recent proposals for sex preselection takes advantage of the assumption that sperm carrying the Y chromosome move faster than sperm carrying the X chromosome. To increase the chances of a male child, semen is collected and placed in a test tube on the top of a dense solution of the protein albumin. The more vigorous Y-chromosome carrying sperm swim through the dense solution toward the bottom of the tube, where they are collected. After washing and concentrating the Y-chromosome carrying sperm, a woman can be artificially inseminated with them.
Other methods of separating the Y-carrying sperm from the X-carrying sperm have as their the goal increasing the chances of engendering a girl. One method for obtaining sperm carrying the X chromosome involves a filtration system on the separation material called Sephadex; during filtration, the heavier X-chromosome carrying sperm reach the bottom of the system first. Sex preselection is a very active area of reproductive research, and undoubtedly many more developments are just around the corner.
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Womens Health
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ALEXANDER TECHNIQUE IN PREGNANCY AND CHILDBIRTH: MISUSE
Originally, when Alexander discovered that he was stiffening his neck and pulling his head back, and creating tension throughout his body, he thought that he was the only person to do this, but his investigations confirmed that this pattern of 'misuse' is common to the vast majority of people.
The effect of this misuse is that it interferes with the head/neck/back relationship, which means that a high degree of muscular tension is needed to maintain upright posture and for movement. This muscular tension is distributed unevenly through the body, with an excessive amount in some areas and too little tension in others, and there is a lack of interaction between the muscle groups. Obviously this brings about the very opposite of what we find with good use: being upright becomes an effort, there is a limited range of movement, the joints are stiff and breathing is impaired.
As with good use, misuse refers to our 'thinking'. It involves performing activities in a habitual and automatic way that is harmful to overall use and functioning. This could mean that we allow our emotional state to affect our musculature adversely, for example if we are worried about something we let tension build up in the neck muscles. Or it could be how we perform everyday activities. Observing people in action, we often see a great deal of effort being used, in parts of the body that are not directly involved in the activity. Check for yourself how tightly you hold your toothbrush while cleaning your teeth - or how tightly you are holding this book right now! You will probably find that, like most people, you are using an excessive amount of effort in holding what is a very light object, and in a task that actually requires a minimum of force.
People misuse themselves in different ways. Broadly speaking, a person may hold himself up with too much tension - the 'sergeant major' approach - or he may 'collapse', with over-relaxed muscles. In practice, of course, it is not as clear cut as this; both forms of misuse involve a combination of excess tension and over-laxity. For example, even in someone with collapsed posture, only some muscles are 'over-relaxed', and therefore others have to work all the harder in compensation, and are over-tense.
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Womens health
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